A metal dust explosion was probably to blame for the blast that tore through a plant in eastern China on Saturday, killing dozens, officials say.
State media said the death toll from Saturday's explosion had risen to 75.
More than 180 other people were hurt in the blast at the car parts factory in Kunshan in Jiangsu province.
State media said at least 25 people died in hospital. The metallic dust stuck to workers' skin, causing extensive burns.
The blast is China's worst industrial accident since a fire at a poultry factory in June 2013 that killed 119 people.
The plant, operated by Kunshan Zhongrong Metal Products Company, polishes wheel hubs for car makers including General Motors.
The company had been warned that high levels of dust in the air could cause an explosion, the South China Morning Post reported, citing the local safety body.
Dust explosions occur when metallic particles contained in an enclosed space are ignited by a spark.
"Very serious dereliction of duty" was behind the accident, Xinhua news agency reported, citing a senior official in charge of the country's work safety, without expanding.