One person was still unaccounted for as of midday Tuesday, Xinhua news agency said, citing local rescuers.

Early reports showed the explosion -- at Baogang United Steel plant in the Inner Mongolia autonomous region on Sunday -- originated from a 650-cubic-metre water and steam tank.

Xinhua previously said 84 people were taken to hospital for treatment following the blast.

Footage on social media showed collapsed ceilings and rubble at the factory, huge plumes of smoke overhead and fire engines at the scene.

Other videos showed an object being blasted into the sky as smoke billowed from the factory and a large, cylindrical hunk of metal that appeared to have come from the plant lying in the rubble of buildings.

Residents kilometres away reported that the explosion shook their homes and shattered windows.

Industrial accidents are common in China due to lax safety standards.

An explosion at a fireworks factory in Hunan province in central China in June killed nine people and injured 26 others.

In 2015, blasts at warehouses containing flammable chemicals in the port city of Tianjin killed more than 170 people and injured 700 others.