Dozens of people are reported to be trapped after a building collapsed early on Wednesday in Leshan city, southwest China's Sichuan Province.

Rescuers have removed more than 30 survivors, who have been sent to three hospitals, from the debris, but no deaths have been reported, said a spokesman for the city's public security bureau.

Part of the former agriculture exhibition center in downtown Leshan collapsed at around 7:20 a.m. when at least 100 people, mostly retirees, were inside to attend a lecture co-sponsored by a health journal and a pharmaceutical company, witnesses said.

"My wife told me there was an accident, so I came out to have a look," said Li Xijian, who lives 50 meters from the site. "Nearly 1,000 people were watching and I couldn't get through the crowd."

Li said he saw people running out of the site, their clothes covered in dust.

The exact number of casualties was yet to be confirmed, said Xu Tianyi, a publicity official with the city government.

Police cordoned the area shortly after the accident. By lunch time, rescue workers were still cleaning the debris and searching for the trapped.

Some people blamed the accident on the heavy rain that hit Leshan in the last two days.

The two-storey exhibition center was built in 1959. It is largely unused except for senior citizens who like to dance in its large halls.