A large fire at Hove Town Hall is believed to have been caused by an electrical fault in solar panels on the roof, the city council has said.
The blaze produced a large column of black smoke that rose over Brighton and Hove.
East Sussex Fire and Rescue Service (ESF&RS) said it had used foam to put out the fire on the roof.
There were no reports of casualties and the building, which was being renovated, was evacuated.
Only a few staff and building contractors were inside at the time
A spokesman for Brighton and Hove City Council said the fire brigade was called at 13:00 BST.
"Everyone was immediately evacuated and no one has been harmed," he said.
"The source of the fire is believed to be an electrical fault with a solar panel on the roof. An investigation is under way."
The council said all its solar panels were checked annually, with those at the town hall checked two weeks ago.
ESF&RS said solar panels were no more dangerous than any other electrical product.
"Anything electrical can develop a fault through any number of reasons," said spokesman Stuart Black.
"We will investigate if that particular brand has had any incidents of fires throughout the UK but I am not aware of any at the moment."