CHANGSHA - Three railway workers remain trapped in a tunnel that collapsed on Saturday in Central China's Hunan province, and rescue efforts are continuing, local authorities announced on Thursday.

Rescuers work to clear off the collapsed debris in the Hongling Tunnel an under-construction Shanghai-Kunming Railway in Xinhua county, Loudi city, Central China's Hunan province, July 4, 2012. [Photo/CFP]

The accident occurred at 7:40 am, when a part of Hongling Tunnel, an under-construction section of the Hukun (Shanghai-Kunming) Railway, collapsed in Xinhua county, Loudi city, the county publicity department said.

The collapsed area was estimated at about 40 meters long, while Hongling Tunnel is 2,625 meters long.

Rescuers have gotten in touch with the workers in the five days they have been trapped underground. Food and water have been sent through ventilation tubing, according to the county publicity department.

It added that three professional rescue groups with about 400 members have been allocated to the rescue.

The cause of the accident is under investigation.