Fire investigators have found traces of accelerant in a health food cafe which was destroyed by a blaze in Sydney's east, New South Wales Police say.

Around 50 people were evacuated from the multi-storey building on Anzac Parade at Maroubra when a loud explosion ripped through the ground floor cafe about 2:00am.

Drew McPherson was among those who heard it.

"It was pretty loud," he said.

"I was probably ... 400, 500 metres down the road and I could hear it pretty clearly.

"It's pretty full on. The shopfront's blown all over the front of the street."

Acting Superintendent Stacey Maloney said police were treating the fire as suspicious.

"At this stage there appears to have been an accelerant used," she said.

Superintendent Maloney said police were currently speaking to the owners of the cafe and that officers wanted to hear from anybody who had information about what triggered the blaze.

"Police are concerned about what's happened," she said.

"There were a number of people who were evacuated as a precautionary measure but police are making inquiries and the community doesn't need to be concerned in relation to this particular incident."

Fire and Rescue Superintendent Paul Johnson said no one was injured in the fire.

"Due to the time of morning, the restaurant itself wouldn't have been open," he said.

"It's going to take further investigations.

"We've handed the area over to police. We've contacted our own fire investigators and I think they'll be working with police in the morning to try to determine the cause."

About 30 firefighters brought the fire under control and it was extinguished.

Residents have since been allowed to return home.