SAITAMA (Kyodo) -- A sinkhole at an intersection near Tokyo that swallowed a truck collapsed further Thursday and merged with a second opening that had formed nearby, as rescue efforts continued into a third day to save the driver.

The sinkhole in Yashio, Saitama Prefecture, has expanded to roughly 40 meters wide and up to 15 meters deep since first appearing on Tuesday, according to local fire authorities. The prefectural government had estimated its width at around 20 meters.

Firefighters plan to deploy heavy machinery inside the hole to remove earth and rubble.

While the trapped 74-year-old man was initially able to speak, communication has been lost since Tuesday afternoon, with the driver's seat of the truck buried in debris.

A sewer pipe running underground in the area was found damaged, leading the prefectural government to start discharging wastewater into the nearby Niigata River late Wednesday as an emergency step to reduce the water flowing into the sinkhole.

The wastewater is treated with chlorine to prevent the contamination of the river. The duration of the operation is undetermined, authorities said.

The discharging of wastewater is unusual, having been carried out on occasions such as the aftermath of the 2011 earthquake and tsunami that devastated northeastern Japan.

Some 1.2 million residents in a total of 12 cities and towns in the prefecture have been urged to refrain from using the sewage system since Tuesday, according to the prefectural government.

"It is inconvenient as the road has been closed for three days," an 83-year-old man who lives near the site said. "I also do not know how much I should refrain from using the sewage system."

Local authorities have called on residents within a 200-meter radius of the area to evacuate, with around 20 people sheltering in a nearby middle school as of Thursday morning.