About 10 Britons are thought to remain at risk in the hostage crisis at a gas plant in Algeria, the BBC understands.
One Briton was killed when militants targeted the desert gas facility, but the fate of others remains unclear.
The Algerian state-run APS news agency says about 60 foreigners are being held, with about 650 hostages freed.
A number of freed Britons have been pictured on Algerian TV, where one said he was impressed by Algerian soldiers who battled with the militants.
Earlier, Prime Minister David Cameron said the number of British hostages is "now significantly reduced" from the previous estimate of "less than 30".
Mr Cameron said Algerian forces which had attempted a rescue were still "pursuing terrorists" at the site.
The Foreign Office says a plane carrying a UK emergency deployment team has landed in the south of Algeria, at an airstrip at Hassi Messaoud, about 280 miles from the besieged BP plant at Tigantourine, near In Amenas.
The BBC's Norman Smith says it is understood this was the closest the Algerian authorities would allow the plane to land.
The plane is to bring home British nationals from the plant, but no details are yet available on how they will be able to travel to the plane.
Speaking to Algerian State Television, one freed Briton, Darren Matthews, said he was "relieved" to be going home, but added: "I won't feel 100% happy until I'm back in the UK."
Another freed Briton is Martin Johnson, from Todmorden in Yorkshire. He is a 62-year-old father of four who works as a motor engineer.
He said: "I think they did a fantastic job, I was very impressed with the Algerian army. I feel sorry for anybody who's been hurt."
And an unnamed Briton who was also freed said the "gendarmes did a fantastic job, kept us all nice and safe and fought off the bad guys. I never really felt any danger, to be honest".
Among those freed earlier were:
- Scottish worker Mark Grant from Grangemouth, who the BBC understands is now with the Algerian army
- The only Northern Irish worker involved, Stephen McFaul, 36, from Belfast, escaped from his captors after the jeep in which he was travelling crashed. He flew to Gatwick and was due to be debriefed at a location in London
Mr Cameron, updating MPs on the situation in Algeria after chairing a meeting of the government's emergency response committee, Cobra, expressed "disgust and condemnation" at the "brutal and savage attack".
He described the attack as "large, well co-ordinated and heavily armed."
He said that while he had had "very good contact over these last few days" with the Algerian authorities, he was "disappointed not to be informed of the assault in advance and we do want to help in any way we can with technical help and assistance".
Algerian troops had attempted to free the hostages on Thursday by storming the residential compound where most were thought to be.
Mr Cameron added: "I think we should show understanding that the Algerian government faces a huge threat from Islamist terrorists and they were facing the situation where there was imminent threat to life and we should bear that in mind."
BP, which owns part of the facility, said there was "a small number" of its employees "whose current location and situation remain uncertain".
The APS news agency cited local officials as saying two Britons and two Filipinos were killed in the military operation, after two other people - a Briton and an Algerian - died on Wednesday when the militants ambushed a bus that was taking workers to the local airport.
The PM said the site was "one of the most remote places in the world" which meant it was difficult to get a full picture of what was happening.
Foreign nationals from at least seven other countries are involved, but precise numbers are not clear.
"Last night the number of British citizens at risk was less than 30. Thankfully we now know that number has now been quite significantly reduced," Mr Cameron said.
US defence secretary Leon Panetta met Mr Cameron on Friday afternoon to discuss the situation. Five Americans caught up in the fighting survived and have now left Algeria.
Algerian Prime Minister Abdelmalek Sellal, speaking about Thursday's action, had told Mr Cameron that the "terrorists had tried to flee, that they [the Algerian forces] judged there to be an immediate threat to the lives of the hostages and had felt obliged to respond."
Mr Cameron said: "When I spoke again to the Algerian prime minister later last night he told me that this first operation was complete but this is a large and complex site and they are still pursuing terrorists and possibly some of the hostages in other areas of the site."
Mr Cameron also said the Algerians were offered British "technical and intelligence support" when the initial attack happened, including hostage negotiation and rescue teams - which was declined.
He added: "We need to be absolutely clear whose fault this is. It is the terrorists who are responsible for this attack and for the loss of life. The actions of these extremists can never be justified."
Labour leader Ed Miliband gave his support to the government and said it was a difficult time for the families of those involved.
He told MPs that "alongside Algerians and other foreign nationals, those involved are British citizens seeking to earn an honest living far from home and their families. It is appalling that innocent and decent people have been targeted in this way".