LANZHOU, Nov. 4 -- Nine workers were buried after a tunnel that was under construction collapsed in northwest China's Gansu Province, said local sources Tuesday.

The accident happened at 3:36 p.m., when about 12 workers were working at the Yangzhouping No. 2 railway tunnel on the outskirts of Lanzhou, Gansu's capital.

A survivor surnamed Ma told Xinhua that they had been some 1,000 meters away from the entrance of the shaft. "We were digging," he said. "Suddenly we heard a big noise and the earth fell in." He escaped with two others.

Rescuers are digging from a nearby shaft in an attempt to find the trapped workers. Three ambulances are standing by at the scene.

The cause of the accident is under investigation.

The railway stretches from Lanzhou to southwest China's Chongqing Municipality and was set to open next year.