More than 300 people have joined the search for six workers missing after a cave-in at a lime powder plant in a karst area of east China's Fujian Province, local authorities said Wednesday.

The accident occurred at about 11:30 a.m. Tuesday at the plant near a village in Xinluo District, Longyan City, a city government spokesman said.

The cave-in area was about 50 meters long, 45 meters wide and 25 meters deep, the spokesman said.

Geological experts believed the cave-in happened naturally as a result of the long-term influence of surface and underground water, he said.

But villagers and workers said the plant's excavation of limestone had damaged the geological structure, triggering the cave-in.

Local authorities would further investigate the cause of the accident, a spokesman of the Xinluo district government said.