Firefighters in southwest China's Guangxi region said Monday afternoon that they are rushing to find four workers who have been buried in concrete after an under-construction plant collapsed nearly two hours ago.

The unfinished manganese plant, located in Tiandeng county of the Guangxi Zhuang autonomous region, collapsed at 2:40 p.m. when workers were pouring reinforced concrete, said an official with the county's fire department.

So far, rescuers have managed to pull out four workers alive, said the official.

There are people still trapped and the number is estimated at four, according to the official.

The plant is owned by the Shagang Manganese Industry Co.