Police and the park owners said they were searching for one worker at the Liseberg Amusement Park in central Gothenburg.

Police evacuated a hotel and offices connected to the amusement park and initially warned households in the area to remain indoors due to smoke. 

According to the Sahlgrenska Hospital, 22 people suffered minor injuries.

Gothenburg’s emergency services said it would take until Tuesday morning to extinguish the blaze, which started at around 10am on Monday.

Images showed exploding fireballs, as flames and several blasts tore up a water slide and a pall of black smoke rose over the city.

“The fire originated at one of the water attractions” outside the water park’s main building “and then spread throughout the building”, Liseberg said in a statement.

The cause of the fire was unknown, however police said the incident was being investigated as a “workplace accident”.

The water park is part of an expansion of the  park and was set to open this year.

News agency TT said reports estimated the cost of the new water park at 1.2 billion kronor ($115 million).

NCC, the construction company building the facility, said work had been ongoing at the site, but they did not know the cause of the fire.