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Just after the sinkhole appeared in Yashio City, just northeast of Tokyo, on Tuesday morning a 3-ton truck fell into it. At first the sinkhole was roughly 10 meters (33 feet) wide and 5-meters (16-feet) deep, but it has since grown to twice that size.

What about the driver?

A 74-year-old man is believed to be trapped in the cabin of the flat-bed truck. He was conscious and communicating with rescue workers earlier but hasn't responded since Tuesday afternoon, according to Yashio fire department official Yoshifumi Hashiguchi.

What caused the sinkhole?

Saitama prefectural sewer system official Jun Uehara said corrosion, possibly because of strong acid constantly passing through the system, might have created a hole in the pipe, causing soil above to fall in and create a large hollow space between it and the road.

No problem was found with the pipe during its last visual inspection, which is required every five years. The sewage water leaking out of the damaged pipe may also cause flooding.

Why is the rescue taking so long?

The unsteady ground, with a hollow space below it, is hampering the rescue. Television footage captured the asphalt road cracking and collapsing into the sinkhole, knocking down billboards. Authorities have tried to save the driver by lifting his truck with cranes, but they could only recover the loading platform, leaving behind the cabin where the driver is believed to be trapped. Officials have also tried without success to remove sediment and dig out the driver. They also flew a drone into the hole to see if rescue workers can climb down, but no progress has been made.

What about the neighbors?

Neighbors are being asked to cut back on water use. Parts of the road are closed. There's also uncertainty about how long the operations will last.

About 20 residents within a 200-meter (656-feet) radius of the sinkhole have taken shelter at a local junior high school Thursday, according to the city.

Over one million residents across the Saitama prefecture, especially in areas where sewage goes to the pipe, have been asked to cut back on laundry and bathing to prevent it from overflowing into the sinkhole. Prefectural officials have also started diverting sewage from an upstream pumping station and release it into a nearby river after treatment, Uehara said.

What's next?

When the driver is taken out, experts will enter the sinkhole and inspect the sewage system.

The Land, Infrastructure and Transport Ministry has ordered a nationwide inspection of sewer systems. In one of the world’s most disaster-prone countries, the sinkhole has raised worries about aging infrastructure.

Most of Japan’s main public infrastructure was built during the rapid economic growth of the 1960s and 1970s. The sewage pipe in Yashiro is about 40 years old.