Images of damage on Rangoon's streets have been emerging
Police are reported to have fired shots at demonstrators. Witnesses said at least one person collapsed.
Witnesses said soldiers stormed six monasteries overnight, smashing windows and doors and beat the sleeping monks.
About 200 Buddhist monks were reported to have been detained during raids on two monasteries in Rangoon.
As protests resumed, only a small number of monks could be seen among the crowd. Many of the protesters were heard chanting nationalist songs.
Key locations of Rangoon democracy protests
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Two members of the National League for Democracy, the party led by pro-democracy leader Aung San Suu Kyi, were also arrested overnight.
There were also reports of raids in the north-east of the country.
The arrests come a day after five people were reported to have been killed when police broke up protests by monks and civilians. The military government has confirmed one death.
Barricades
In Rangoon, security forces have set up barbed wire barricades around Shwedagon Pagoda and Rangoon city hall, two of the focal points for the demonstrations.
The junta are using dirty tactics - they don't fire guns but beat people with rifle butts
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The British ambassador in Rangoon, Mark Canning, said soldiers and police had stepped up their presence.
"There are truckloads of troops in a number of locations - more than there seemed to be yesterday," he told the BBC.
"There are fire trucks, water canons positioned in a number of places - there are about three of them outside city hall. There are a number of prison vans also to be seen in certain places."
Leaflets have been circulated throughout Rangoon urging people to come out and show solidarity with the monks.
UN debate
There are no indications yet that the military government is ready to listen to the many calls for restraint being made around the world, says the BBC's South East Asia correspondent Jonathan Head.
On Wednesday, the UN Security Council held an emergency meeting in New York and called on the military junta to show restraint - a call also made by China on Thursday.
The US and European Union wanted the council to consider imposing sanctions - but that was rejected by China as not "helpful".
Instead, council members "expressed their concern vis-a-vis the situation, and have urged restraint, especially from the government of Myanmar," said France's UN ambassador Jean-Maurice Ripert.
They welcomed a plan to send UN special envoy Ibrahim Gambari to the region, and called on the Burmese authorities to receive him "as soon as possible".
China and Russia have argued the situation in Burma is a purely internal matter. Both vetoed a UN resolution critical of Burma's rulers in January.
Analysts fear a repeat of the violence in 1988, when troops opened fire on unarmed protesters, killing thousands.
The protests were triggered by the government's decision to double the price of fuel last month, hitting people hard in the impoverished nation.
Monks protest in Myanmar, September 24, 2007. 
At least 200 monks have been arrested in Myanmar during night-time raids on monasteries not long before sunrise. Government forces began to crack down on protesters after several days of peaceful demonstrations, but despite the violent treatment from military personnel, the monks returned to the streets in the morning.

100 monks were taken by security forces when they raided a monastery at Ngwe Kyaryan. "Only two or three sick monks were left behind", a witness near the monastery said. Some reports state that shots have been fired at demonstrators, with one "collapsing", but it's not known if the individual was shot.

"There are fire trucks, water cannons positioned in a number of places - there are about three of them outside city hall. There are a number of prison vans also to be seen in certain places", said Mark Canning, the British ambassador in Rangoon.

The United States and European Union have said that they are deeply troubled by events, issuing a statement calling on the United Nations Security Council to consider sanctions, but China and Russia do not believe sanctions will "be helpful" and immediately dismissed the call, calling the situation a matter for the "internal government" of Myanmar.
 
"France will not accept the gagging of Burma's opposition", said Nicolas Sarkozy, the French President, who also said that "the Security Council expressed their concern vis-a-vis the situation, and have urged restraint, especially from the government of Myanmar."