Mr Blair, speaking during his visit to Beijing, said: "It's been really tough for people, I know that, but it's been tough for our officials on the ground."
His comments came as the Foreign Office claimed that British diplomats had been unable to get into New Orleans until Sunday. A spokesman said more than 20 diplomats had been willing to go but requests for permission from the US state department and the Louisiana state government had been repeatedly rebuffed.
Mr Blair said: "I'm really sorry if there have been difficulties about this but I can assure you some of these staff have been working round the clock and because it's been a very difficult and confused situation it's been difficult for them, the staff, as well as the people for whom this has been a catastrophe."
Although journalists have been going in and out of New Orleans, the Foreign Office spokesman said the journalists had a choice but "we have to work with the US authorities as accredited diplomats and we were told no one was getting access.
"We were told ... that it would hamper the evacuation."
He added: "The security situation was not great. If you had put in diplomats, it would have needed armed guards and that would have taken away resources [from the rescue effort]."
The spokesman said diplomats had been in the surrounding cities, and had offered to help Britons with accommodation and clothes - paid for by the Foreign Office - and with flights.
Nine officials from the Foreign Office rapid deployment team had flown to the US on Thursday to support British staff converging on the hurricane-hit area from around the US.
"When we were made aware there were Britons in the Superdome, we raised the conditions with the US authorities and not long after that they were moved."
Britons caught up in the hurricane continued to arrive back in the UK yesterday. One family said American police took snapshots of trapped tourists instead of helping them.
Gerard and Sandra Scott were stranded in their New Orleans hotel with their young son but police did nothing as they shouted for help from the hotel windows. "I couldn't describe how bad the authorities were," Mr Scott told Radio 4's World at One. "Just the little things like taking photographs of us ... for their own personal photo albums, little snapshot photographs.
"At one point, there were a load of girls on the roof of the lobby saying 'Can you help us?' and the policemen said 'Show us what you have got' and made signs for them to lift their T-shirts. When they said no, they said 'Fine' and motored off down the road in their motorboat."
Several Britons have yet to make contact with their families, including Mike Healy, 48, originally from Warwickshire but now living in Bay St Louis. His sister, Susan Betteridge, 52, of Stratford-on-Avon is planning to fly out to look for him.
Jill Amend, 70, from Richmond, south-west London, was waiting for news of her son, Vernon Carroll, 46, who she fears she may have seen floating face down in the flooded city on television news.
"I know he would call me if he could," she said. "I wish the Foreign Office could be a bit more supportive ... All I can do is sit here, wait and worry."
British Prime Minister Tony Blair has apologised to Britons affected by Hurricane Katrina. Many British citizens who were trapped in the New Orleans have complained to the British Foreign Office about the lack of response from their government after the hurricane destabilized almost 200 miles of the United States gulf coast.

British nationals living and vacationing in New Orleans reported that U.S. authorities had refused to evacuate them as Hurricane Katrina approached the city, leaving them stranded in their hotels.  President George W. Bush has been criticized for refusing material aid from France and Britain in rescuing people trapped in New Orleans.