Armed police were sent to guard key locations in Islamabad
Bhutto's reaction
Shaukat Aziz told a news conference that the government remained committed to the democratic process.
But he said parliament might change the date of elections planned for January, and gave no end date for the emergency.
Rights have been suspended, media has been restricted and hundreds of people arrested under the emergency decree.
Mr Aziz said 400 to 500 "preventative arrests" had been made so far, and said the emergency, imposed by Gen Musharraf on Saturday, would last for "as long as is necessary".
Small protests have started in the capital, Islamabad, where police and security forces are on the streets surrounding key sites.
Obviously we are going to have to review the situation with aid
Condoleezza Rice, US Secretary of State
The moves came as the Supreme Court was due to rule on the legality of Gen Musharraf's October election victory.
US Secretary of State Condoleezza Rice has said Washington is reviewing the aid which it gives to Pakistan in the wake of Gen Musharraf's decision.
"Obviously we are going to have to review the situation with aid, in part because we have to see what may be triggered by certain statutes," Ms Rice said.
In recent years Gen Musharraf has been a key ally in Washington's war on terror and has received about $10bn in aid since 2001.
"Some of the aid that goes to Pakistan is directly related to the counterterrorism mission," Ms Rice said, adding that that complicated the issue.
Threat of force
After a calm start to Sunday, a few dozen people staged a brief protest near the parliament building in Islamabad before police moved in to break up the gathering.
HAVE YOUR SAY The world is entering into 2008 and still we are at 1958
Nasir, Islamabad
Your views on emergency West faces new dilemma
More protests are expected throughout the rest of the day, he adds, with police appearing ready to use force against unauthorised demonstrations.
Tough new media restrictions are controlling the news available throughout Pakistan: all non-state TV stations and some radio channels have been taken off the air, as have international services such as BBC World TV.
Independent newspapers have been allowed to continue publishing, but Gen Musharraf's decree severely limits what they can report.
Local newspapers and key opposition leader Benazir Bhutto accused Gen Musharraf of bringing in martial law without formally declaring it.
But Pakistan's attorney general said the prime minister and parliament remained in place and the civilian government would continue to function.
Opposition anger
Among the hundreds of people arrested since the declaration was Javed Hashmi, acting head of former Prime Minister Nawaz Sharif's Pakistan Muslim League.
Gen Musharraf, he said as he was taken away, would pay a price for his decision to restrict freedoms.
"Musharraf's days are numbered. Time has come to end the political role of the army."
EMERGENCY RESTRICTIONS Constitutional safeguards on life and liberty curtailed Police get wide powers of arrest Suspects can be denied access to lawyers Freedom of movement restricted Private TV stations taken off air New rules curtail media coverage of suicide bombings or militant activity Chief justice replaced, others made to swear oath of loyalty Supreme Court banned from rescinding emergency order
In pictures: Emergency rule Declaration: Full text
Ms Bhutto, who recently returned to Pakistan from self-imposed exile, flew back to Karachi from a trip abroad upon hearing news of Gen Musharraf's decision.
She confirmed that troops were not surrounding her Karachi home, contrary to some earlier reports, and laid out her demands for the holding of free and fair elections.
"We the political parties are calling for the restoration of the constitution, and for the holding of the elections under an independent election commission," she told the BBC.
There is no word yet whether she plans to enter dialogue with the president or to lead opposition to his rule.
President defiant
In a TV address on Saturday evening, Gen Musharraf explained his decision, saying the current situation had forced him into making "some very painful decisions".
"Extremists are roaming around freely in the country, and they are not scared of law-enforcement agencies," the president said.
"Inaction at this moment is suicide for Pakistan and I cannot allow this country to commit suicide."
Court issue
Following the announcement of emergency rule, the country's chief justice was replaced and the Supreme Court surrounded by troops.
Gen Musharraf moved quickly to appoint a new chief justice
The Supreme Court was to decide whether Gen Musharraf was eligible to run for re-election last month while remaining army chief.
Fears were growing in the government that the court could rule against Gen Musharraf.
Pakistani lawyers announced they would strike on Monday in protest at the president's decision.
Pervez Musharraf in 2004. 
Hundreds of people were rounded up by security forces in Pakistan, one day after Pervez Musharraf declared emergency rule, effectively martial law. Scores of opposition figures were among those detained.

Javed Hashmi, a leader of the Pakistan Muslim League (N) party, the party of exiled former Prime Minister Nawaz Sharif, was arrested. "Musharraf's days are numbered. The time has come to end the political role of the army," he told reporters in Multan before being taken away by police. Nawaz Sharif said to an Indian news channel: "We have not witnessed such a grave situation in the 60 years of Pakistan's history."

Also arrested were pro-democracy attorney, Munir Malik, and the leader of the Human Rights Commission of Pakistan, Asma Jehangir. Both have been involved in protests against Musharraf in past years. Troops also arrested the staff of the Commission and began to close off and surround government buildings.

Former Prime Minister Benazir Bhutto, who recently returned home, addressed supporters in Karachi. "This is a situation worse than an emergency. The people of Pakistan will not accept this," Bhutto said.

On Saturday, Musharraf laid out his reasons for the emergency rule. "Please do not expect or demand your level of democracy, which you learned over a number of centuries. Please also do not demand or expect your number of civil rights, human rights or civil liberties … Please give us time. For me and every Pakistani, Pakistan comes first," said Musharraf in a statement.

In a "charge sheet" levied against the judiciary, the government said: "... (T)here has been increasing interference by some members of the judiciary in government policy, adversely affecting economic growth, in particular," adding that there was "constant interference in executive functions."

The government further accused the judiciary of having "weakened the writ of the government, the police force ... been completely demoralised and ...fast losing its efficacy to fight terrorism, and intelligence agencies ... thwarted in their activities and prevented from pursuing terrorists."

Parliamentary elections may be delayed. The current Prime Minister, Shaukat Aziz said, at a news conference, that the government is still committed to democracy, but "the government is deliberating on the election schedule."

"Now that we have emergency rule, parliament's term can be extended by one year," said Aziz. Pakistan was due to have a general election on January 15, 2008.
Presidential Palace on June 27, 2007.
Meanwhile, the United States has said it will review the financial aid that is providing Pakistan. United States Secretary of State Condoleezza Rice told reporters, while in Jerusalem: "Obviously we are going to have to review the situation with aid, in part because we have to see what may be triggered by certain statutes."

The US has given an estimated US$10 billion in aid to Pakistan since 2001, primarily for counter-terrorism. This year Pakistan is receiving about $700 million in assistance.

"We have to be very cognizant of the fact that some of the assistance that has been going directly to Pakistan is directly related to counter-terrorism missions. This is a complicated matter," Rice said. She also condemned the declaration of emergency rule, saying "it's highly regrettable that Pakistan's president has declared a state of martial law. The U.S. does not support extra constitutional measures."

US Senator Joe Biden, the chairperson on the US Senate Committee on Foreign Relations agreed that a review is needed. "I'm not sure how much good that military aid we're giving him to fight the extremists is doing us anyway," he said on television program, ''Face the Nation''.

Tony Blair, special envoy for the Quartet on the Middle East said on ''Late Edition with Wolf Blitzer'': "The sooner that we return to the pledges to restore democracy that were set out, the better. But it's a very, very difficult situation this indeed, and it's a situation that if it's not resolved in the right way, I think it's extremely worrying for the whole of the world, not just for Pakistan."