Two of the four people seriously injured in a Friday morning explosion at a disinfectant factory in northeast China's Heilongjiang Province died Friday afternoon, local officials said.

Two of the injured succumbed around 3:30 p.m., while the other two injured were still in critical condition Friday afternoon, according to doctors at the No. 5 People's Hospital in the provincial capital of Harbin.

The survivors sustained burns to 95 percent of their bodies and are suffering from smoke inhalation as well, the doctors said.

The disinfectant plant, Harbin Kaile chemical factory, in Xiangfang District is privately owned, said Sun Hengyi, deputy secretary of the district's committee of the Communist Party of China.

An initial investigation showed that the blast was caused by fire. The factory used sodium nitrite, which combusts at a temperature of 175 degrees Celsius, as its main raw material for manufacturing disinfectant, according to chemical experts at the site.

Police have cordoned off the factory. An investigatory team has been formed to uncover the cause of the blast, Sun said.

Residents living near the factory have been evacuated.