Rescue officials are working to stop water from flowing into a sinkhole north of Tokyo, as it could hinder their search for a truck driver trapped in the hole.

A truck, driven by a 74-year-old man, plunged into the sinkhole when the ground suddenly gave way at an intersection in Yashio City, Saitama Prefecture, on Tuesday.

A nearby section also later caved in, and the sinkhole expanded as the two holes merged. The officials say the cavity is about 15 meters deep, with mud and other debris believed to be piled up to a height of around 8 meters.

The truck driver's condition remains unknown.

The rescue team began digging a slope on Thursday to enable heavy machinery to enter the sinkhole to clear away the muddy rubble.

Workers are reinforcing the ground as they dig the slope, which is expected to be about 30 meters long and 4 meters wide. Work has continued overnight, and the slope is expected to become usable in a few days.

Prefectural officials believe the first collapse was caused by the rupture of a sewage pipe roughly 10 meters underground. They say rainwater and other forms of water are flowing into the hole.

The rescue team is working with prefectural officials to quickly locate the source of the flow and find ways to stop it.