Two firefighters and a member of the public have died in a large fire in Bicester, the fire service announced.
The firefighters died while fighting the inferno at a former RAF base in Oxfordshire, which now hosts Bicester Motion, home to classic car restoration and engineering businesses.
The London Fire Commissioner, Andy Roe, revealed one of the deceased firefighters was a leading London firefighter and sub-officer who was on "retained duty" with the Oxfordshire Fire and Rescue Service (OFRS).
The second firefighter was part of the OFRS.
Bicester Motion said in a statement "a close friend of the site" also died in the blaze.
The local fire service was called to the scene at 6.39pm last night.
Chief Fire Officer Rob MacDougall said: "It is with a very heavy heart that we today report the loss of two of our firefighters. Families have been informed and are being supported.
"Our thoughts are with them at this most difficult of times and we ask for privacy to be respected."
Mr MacDougall appeared to hold back tears during a news conference this afternoon as he talked about how "proud and grateful" he is for "the unwavering bravery demonstrated by all the emergency services personnel".
Two other firefighters sustained serious injuries and are currently being treated in hospital, Oxfordshire County Council said in a statement.
Ten fire crews attended the blaze and three remain at the scene, with the fire now under control, the fire service and council said.
Thames Valley Police have launched an unexplained death probe.
Assistant Chief Constable Tim Metcalfe said: "We will have additional officers at the scene for a number of days to come, so if you have any concerns please speak to us.
"We have commenced an unexplained death investigation, led by our major crime team.
"This is currently not a criminal investigation, but we will follow the evidence as our inquiries continue.
"We will continue to have officers at the scene for a number of days to ensure the public remain safe.
Footage shared on social media shows black plumes of smoke billowing into the sky and flames swallowing the large building.
Kieran McGurk, who lives opposite Bicester Motion, said he heard "multiple explosions" and "loud bangs".
Another resident, who gave her name only as Ellie, said she saw a "big black plume of smoke" coming out of the Bicester Motion buildings on Thursday night.
"I heard loads of pops and crackles and bangs. It was quite bad," she said.
Ten fire crews attended the incident, with four remaining at the scene. The blaze is now under control.
Police officers erected a cordon and remained at the entrance to Bicester Motion on Friday, while a fire engine and ambulance could be seen leaving the scene.
Local residents were asked last night to remain indoors and keep their windows shut, but this advice has now been lifted.
Bicester Motion, which was formerly known as Bicester Heritage, said in a statement: "There are no words at times like this, but our thoughts and prayers are with (the victims') families and loved ones.
"We pray for the two firefighters in hospital. The bravery shown by the emergency services teams has been overwhelming.
"We are grateful for all the support and especially the exceptional work by all in such unprecedented circumstances."
Prime Minister Sir Keir Starmer said the deaths in the blaze were "devastating news", adding he hopes "those in hospital make a full and swift recovery".
Tory leader Kemi Badenoch also paid tribute, telling reporters at the Welsh Conservative conference in Llangollen: "My heart goes out to the families of those people who have lost their lives and those who are still on the front line, because I understand the fire is still going, and I hope that we can get to the bottom of exactly what's caused this and make sure that it doesn't happen again."
Oxfordshire MP Anneliese Dodds paid tribute to the victims in a House of Commons speech, saying she wanted to convey her and Bicester and Woodstock MP Calum Miller's "deep sorrow and solidarity with the families of those who have died, and our fervent and heartfelt best wishes to the two firefighters who remain in a serious condition".
"We're grateful for their heroism and that of their colleagues when, as ever, they run towards danger to serve us all," she added.
Mr Miller said in a statement he was "heartbroken" to learn about the deaths and that "this is a devastating moment for our community".
The Bicester airfield, which is "the most complete and strongly representative example of an RAF airbase," according to Historic England, will remain closed over the weekend.
(c) Sky News 2025: Two firefighters and one other person die after fire at former RAF base in Oxfordshire