The blaze at the Oceana water park in the popular Liseberg amusement complex in downtown Goteborg spread across several water slides and a hangar-like building. Police and fire officials could not immediately say what caused the fire.
Police said 12 people were slightly injured.
A nearby hotel and office facilities were evacuated.
Oceana had been scheduled to open this summer, Swedish news agency TT said, adding that it cost 1.2 billion kronor ($10.6 million) to build.
pll/mem/ehl
