Hundreds of rescuers searched Thursday for about 20 people believed still trapped under the rubble of a large chimney that collapsed on workers at a power plant in central India, killing at least 35.

It was unclear if any of those missing were still alive after the accident Wednesday in which the 820-foot-tall chimney came crashing down on the plant's cafeteria as the workers had tea. The plant is under construction.

"There may be some lucky ones," said R.K. Vij, inspector-general of police. It was uncertain how many were in the cafeteria at the time of the accident, he said, although about 100 people were at the work site.

The power plant, owned by Bharat Aluminum Co., or BALCO, was being built by a Chinese company with the help of local contractors in Korba, about 600 miles southeast of New Delhi.

"Continuous heavy rains and lightning at Korba in the past few days is understood to be a probable reason for this incidence," Gunjan Gupta, the chief executive officer of BALCO, said in a statement. "However, the exact reasons for this incidence would be known only after the inquiry."

Twenty-one bodies were recovered Thursday, after 14 were found Wednesday, said Vivek Sharma, a police officer at the site. Seven people were hospitalized with injuries, he said.

Rescuers using cranes and saws will need at least another half day to clear the mound of rubble consisting of big chunks of concrete slabs and twisted steel, said Vishwa Ranjan, director-general of police in Chhattisgarh state, where the accident occurred.

Raman Singh, the top elected official in Chhattisgarh, ordered an investigation into the accident.