SHANGHAI, Dec. 6 -- Three people were confirmed dead and four others injured after a blast at a garbage incinerator in Shanghai on Thursday, local safety authorities said Friday.

The blast occured in a workshop at the Shanghai Jiangqiao garbage incinerator on Thursday afternoon while maintenance work on pipelines at the plant was underway. Some 250 square meters of the workshop roof collapsed, according to the Shanghai work safety bureau.

Of the injured, three are in a serious condition.

Shanghai has set up an investigation team to look into the accident. Meanwhile, a survey of environmental effects is underway.