Super spicy chili sauce being cooked at a London Thai restaurant sparked road closures and evacuations after passers-by complained that the smell was burning their throats, police said Wednesday.

London Fire Brigade's chemical response team was called after reports that a strong smell was wafting from the restaurant in the heart of London's Soho district Monday afternoon, a Metropolitan police spokesman said, speaking anonymously in line with force policy.

Authorities sealed off several premises and closed roads. The Times of London described shoppers coughing and spluttering as firefighters wearing special breathing masks sought the source of the smell.

The paper said firefighters smashed down the door of the Thai Cottage restaurant and seized extra-hot bird's eye chilis which had been left dry-frying. It said they were being prepared as part of a batch of Nam Prik Pao, a spicy Thai dip.

"The smoke didn't go up into the sky because of the rain and the heavy air," The Times quoted Thai Cottage owner Sue Wasboonma as saying. "It's the hottest thing we make."

The police spokesman said no arrests were made in the case.

"As far as I'm aware it's not a criminal offense to cook very strong chili," he said.