A 74-year-old truck driver was swallowed by the cavity on Tuesday, which has since expanded to 40m across – almost the length of an Olympic swimming pool.

The growing hole could be the result of corroded sewer pipes, according to local authorities.

Requests were issued for five households near the hole in the city of Yashio, Saitama, to take shelter on Sunday, a local government official told AFP.

This is on top of other residents within a 50m radius of the cavity, who are also being encouraged to evacuate, he said.

On Saturday, Japanese rescuers completed building a 30m slope to send heavy equipment and reach the truck driver.

However, a good amount of sewage water was discovered underneath the slope, which, combined with rain, led to the rescue mission being suspended on Sunday, public broadcaster NHK said.

With the walls of the hole – around 15m deep, according to NHK – eroding, rescue workers are unable to stay inside it for long.

The hole was initially around 5m in diameter but combined with a larger cavity that opened during the rescue operation on Tuesday night.

Around 1.2 million people living nearby have so far been asked to cut back on showers and laundry to prevent leaking sewage from hindering the operation.