Baku, May 16, AZERTAC Seven workers, who were wounded after a factory wall accidentally collapsed in Shanghai Thursday, have died in hospital, authorities said, Xinhua reported.As of 6:10 p.m. Thursday, 21 people had been pulled out of the debris and rushed to hospital. Of them, seven died after ineffective treatment.Two were known to be still trapped in the ruins.The wall fell at 11:20 a.m. Thursday on Zhaohua Road in Shanghai's Changning District, trapping an unspecified number of people at the site, according to the municipal bureau of emergency management.The accident occurred when the factory building was being demolished.The accident is under investigation as rescue efforts continue.