A four-storey block of flats has been "badly damaged" after its roof caught alight.
The fire broke out at Osbourne House in Imperial Avenue, Westcliff-on-Sea, Essex, at 12:12 BST on Tuesday.
"The roof of the building has been completely destroyed," said the Essex fire service, adding 16 properties inside had been affected.
An investigation is due to determine the cause of the fire, which was under control by 14:00.
Alex Smithyes, who lives close to the building, said it was "quite shocking" to watch the blaze unfold.
"I could see the fire creeping under the tiles of the roof and then all of a sudden the whole roof collapsed in," he said.
"It was very, very unexpected and it all happened quickly."
Firefighter Rick Williams said Southend City Council was helping to rehome those affected, but nobody had been injured.