Police have detained four residential building owners after their rented structures collapsed, killing 22 people in Wenzhou, Zhejiang province, on Monday.

About 800 rescue workers finished the search in Lucheng industrial district on Tuesday.

Police are investigating the cause of the collapses.

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 rundown residential structures were all rented to migrant workers.

Yan Yongfa, a migrant worker from 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 with a low rent of 420 yuan ($63) 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 structures originally had four stories, but the owners converted them to five or six stories.

"The old buildings were part of the government's urban plan for reconstruction," he said.

After the buildings collapsed, several streets were cordoned off.

Zhang Geng, mayor of Wenzhou, vowed on Tuesday that the city government would thoroughly check all rundown residential buildings 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 the buildings and ground had been soaked by rainwater, partly contributing to the collapse.

(China Daily 10/13/2016 page4)