An aerial photo taken on March 22 shows the site of a factory explosion at a chemical industrial park in Yancheng, Jiangsu province. (Photo: China Daily)

Six employees of Jiangsu Tianjiayi Chemical Co. and its controlling shareholder Nijiaxiang Group have been put under criminal coercive measures for their roles in a chemical plant blast in East China's Jiangsu province, local authorities said Saturday.

So far a total of nine people have been put under criminal coercive measures, which may include summons by force, bail, residential surveillance, detention or arrest.

The explosion happened at about 2:48 pm on March 21 following a fire that broke out in a chemical industrial park in Xiangshui county. Seventy-eight people were killed in the blast, and 187 are still receiving treatment in hospitals.