Around 700 people have been evacuated from Kiwi House, New Zealand's Games hospitality site after a fire broke out.
Emergency services are in attendance at Kiwi House near King's Cross in central London after a gas canister being used for a barbecue exploded.
Hundreds of New Zealanders who have come to London for the Games had gathered for a party before the blaze started.
Brook Johnstone, 55, from Port Waikato, said: "I looked around and the gas bottle had a little flame around it. The cook was trying to put it out and the flame just got bigger so I just said 'Let's get out of here'.We got inside and everyone was evacuated."
Mr Johnstone, who is in London on holiday, said the canister exploded with such force that it blew the roof off the barbecue area.
New Zealander and Leeds University student Sonia Holland said she did not believe anyone was injured in the blaze.
The 19-year-old, from Napier, said: "I literally just got my food and there was a big kerfuffle around the barbecue area. Then everyone was pushed inside but then people were telling us to get out of the building. They got everyone out of the building as fast as they could. I was out within two minutes."
She said when she looked back at the building she could see fire and smoke coming from the garden of the building. Ms Holland, who is also working as a volunteer Games Maker at the Olympics, added that she was not aware of any athletes in attendance.
A spokesman for London Fire Brigade said the blaze broke out just after 7.20pm. He said that before crews arrived two gas cylinders were believed to have exploded. Ten firefighters are controlling the blaze and a cordon has been put around the building in case another canister explodes.
Kiwi House is self-described as a "haven" for friends, family and supporters of the New Zealand Olympic team.