HANGZHOU -- Police have detained four house owners after their leased residential buildings collapsed, killing 22 people in Wenzhou city in East China's Zhejiang province Monday.

About 800 rescue workers finished the search, in Lucheng industrial district on Tuesday, pulling 28 people from the debris. Twenty-two were found dead, and six survivors were hospitalized.

Police are investigating the cause of the disaster.

The four buildings were built by Zhongyangtu villagers in the 1970s and 1980s. Five adjacent houses built in the same period remain standing, but rescue workers are now demolishing them to avoid further disasters.

The run-down residential houses were all leased to migrant workers.

Yan Yongfa, a migrant worker from southwest China's Guizhou Province and one of the six survivors, said he was asleep when there was a huge bang, and he was plunged into debris. He said the old village houses were attractive to migrant workers as rent was low at 420 yuan ($62.5) per month.

Western Wenzhou is an industrial cluster that attracts many rural laborers looking for work.

A migrant worker surnamed Zhang said he has worked in the area for 19 years. Many of the village houses originally had four stories, but house owners have now converted them to five or six stories.

"The old buildings have been under the government urban planning for reconstruction," he said.

After the buildings collapsed, several streets were cordoned off.

Zhang Geng, mayor of Wenzhou, on Tuesday vowed that the city government would make a thorough check on all run-down residential houses and start reconstruction as soon as possible.

Wenzhou was affected by strong rainfall brought by Typhoon Meranti, the strongest storm of the year, in September. Rescue workers said that the houses and the ground had been soaked by rain water, partly contributing to the collapse.