Divers have been dispatched in the search for 14 workers missing since water flooded a tunnel under construction in southern China three days ago, authorities have said.
Zhang Yisheng, the vice mayor of Zhuhai city, told a news conference that the water level in the tunnel had dropped by 11.3 metres (37ft), according to an online report by state broadcaster CCTV.
Underwater robots, unmanned ships and sonar detectors would also be deployed, Mr Zhang said.
Search teams have been slowly advancing into the tunnel as water is pumped out. As of Sunday morning, they were about 600 metres into the tunnel, a little more than half the 1.1-kilometre distance to where the workers were trapped.
That is the length of the 1.8-kilometre tunnel that has been dug so far.
Their advance has been slowed by carbon monoxide fumes from machinery being used in the tunnel as part of the operation, though the level of the potential deadly gas has been lowered by improving ventilation.
The flood happened about 3.30am on Thursday. An abnormal noise was heard and bits of material started falling off on one side of the two-tube tunnel.
An evacuation was ordered but water rushed in and flowed through a connection into the other tube of the tunnel, trapping 14 workers on that side.
The tunnel lies under a reservoir, but the cause of the accident is still under investigation.
In March, two workers died in another part of the tunnel when a protective wall collapsed and they were hit by falling stones, according to a notice from the Zhuhai emergency management department.
Zhuhai is a coastal city in Guangdong province and near Macao at the mouth of the Pearl River delta. It was one of China’s early special economic zones when the ruling Communist Party started opening up the nation’s economy about 40 years ago.