Cause of a three alarm beach hotel fire Sunday at the height of the Fire Prevention Week observance has not yet been determined according to Acting Fire Chief Robert Fitz.

The Four-story Tides Hotel on Ocean Blvd. burst into flames shortly after 3 p.m. Sunday afternoon while Hampton firefighters were assembled uptown at the High Street Parking lot demonstrating firefighting techniques and equipment.

Because the firemen were all suited up and ready to go, Chief Fitz said the department was able to respond to the fire with more men than usual. In addition, the North Hampton ladder company was already in town for the fire prevention demonstration and was able to respond immediately to the fire.

According to the chief, the building owned by George Callahan of Westford, Mass. was unoccupied at the time and origin of the fire has been pinned down to the first floor area.

Seabrook, Exeter, Hampton Falls and North Hampton responded to the mutual aid call.

Chief Friz reported that for the first time in many years the "salt water fire system" was put into effect. The system, although still called by that name, was converted to fresh water by the Hampton Beach Precinct a few years ago and Friz reported that the water pressure was excellent.

Firefighters were able to contain the blaze to the hotel structure despite the fact that the Grub and Grog restaurant is located close to the North side of the hotel.

During the blaze a false alarm was pulled at a box on the corner of D Street and Ocean Blvd., the chief said.

The all-out was sounded at 8:41 p.m..