LONDON (AP) — Safety checks conducted after the deadly London high-rise fire have revealed that four tower blocks in the city are at risk of collapse if there is a gas explosion.

Local officials say the Ledbury Towers housing complex in south London has a design flaw that leaves them vulnerable.

The flaw should have been fixed after a similarly designed London tower collapsed in 1968, killing four people. But Southwark Council says the work may never have been done.

The council said Friday it has turned off the gas supply to the buildings, which contain 242 apartments. It says residents will have to move out during emergency repair work.

Thousands of buildings are being checked for safety after the June 14 fire at Grenfell Tower, which killed at least 80 people.