An explosion occurred at a cardboard factory in Finland.
A pulp tank used to prepare raw material for paper and cardboard exploded.
The 30-metre-high tank had a system for maintaining pressure and mixing, writes the Yle newspaper.
The investigation will be carried out by the police and the State Centre Otkes, which specialises in major accidents.
The explosion occurred after a sudden increase in pressure inside the tank.
As a result of the strong exhaust, the tank lid was thrown to a height of about 20 meters.
The roof of a plant in the city of Kuopio collapsed over an area of 600 square meters.
The plant's general director, Juha Koukka, said the incident came as a surprise to him.
The extent of material damage to the enterprise is still unknown.
Otkes will continue to examine the scene to gather information for further investigation.
