GOTHENBURG, Sweden, Feb 12 (Reuters) - A powerful fire broke out at an amusement park in the western Swedish city of Gothenburg on Monday, engulfing outdoor water slides and related facilities that were under construction, eyewitnesses and rescue services said.

There were no reports of serious injuries, but police said on Monday evening that one man was missing.

No guests were at the Oceana waterpark, a new addition to Gothenburg's Liseberg funfair, which had been scheduled to open later this year, a spokesperson for the park told Swedish news agency TT.

The park said in a statement that the man missing had been working on the project on behalf of Liseberg.

"The fire started at one of the water rides outside the building and then spread to the entire building," Liseberg said in its statement.

Efforts to extinguish the fire were still ongoing at 1700 GMT and were expected to take time, regional newspaper Goteborgs-Posten reported.

Thick black smoke rose above the city and police advised those living in the area to stay indoors and keep windows closed to protect against fumes.

Live video showed slides being engulfed by flames while several fire-fighting vehicles surrounded the area.

Guests at a nearby hotel and office premises had been evacuated, Liseberg said. (Reporting by Johan Ahlander; writing by Stine Jacobsen and Marie Mannes; editing by Terje Solsvik and Leslie Adler)