Fire investigators will be going into a building in central London later to find out what caused a blaze there.
A spokesman for the London Fire Brigade (LFB) said 75 firefighters tackled the fire in Field House in Chancery Lane.
He said about 75% of the roof of the building, which houses the Asylum and Immigration Tribunal, had been damaged.
About 130 people had to be evacuated from the building, which was being refurbished, after the fire broke out on Wednesday afternoon.
The LFB spokesman said three 2.3 stone (15kg) propane cylinders had been found on the roof of the building but the fire was now "surrounded and under control".
"We have an extensive salvage operation on floors up to the fourth floor," he said.
Parts of two other adjacent buildings also had to be evacuated, the LFB spokesman said.
A Tribunals Service spokeswoman said all hearings due to take place o
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