The government of Saitama Prefecture, north of Tokyo, says searchers have found what seems to be the cab of the truck that fell into the hole two weeks ago. It says the driver is likely to be inside.

The sinkhole developed on January 28, causing a road to collapse.

Officials sent drones into a sewage pipe under the hole. They found waste water streaming through gaps in asphalt rubble and other debris piled up in an area upstream from the cabin. The sewage level around it is now about 1.6 meters deep.

They are planning to install a pipe upstream from the cabin to bypass the waste water. This project will take about three months to complete.

A former firefighter says reducing the amount of sewage and hydrogen sulfide will help the search.

He said the air inside the pipe can kill after just one or two breaths, but firefighters would be able to operate down there if the levels drop.

Similar sinkholes have appeared in other areas in Japan. Water is gushing out of a 2-meter-wide hole which opened in Chiba Prefecture, east of Tokyo. The hole is believed to have formed as water leaked from a ruptured underground pipe.

Japan's infrastructure ministry has ordered seven prefectures with similar sewage pipes to carry out emergency inspections.