TAMPA, Fla. (Reuters) - Police have given the all clear at the Legoland amusement park and hotel in Winter Haven, Florida, after it was evacuated on Thursday due to an anonymous bomb threat that park officials later said they considered a hoax.

The written threat was received shortly before noon, and all guests were evacuated in less than an hour, the Winter Haven Police Department said. Police gave the all clear to park officials around 5 p.m. local time (2100 GMT), saying no explosives were found.

"At this time, we believe this is a hoax, but we take all threats seriously," said Adrian Jones, general manager of Legoland Florida Resort, in a statement. He said the decision to evacuate "was made in an abundance of caution at the advice of law enforcement."

The theme park owned by Merlin Entertainments <MERL.L> remained closed for the day as police investigated. The park will reopen at its regularly scheduled time on Friday morning and visitors staying at the hotel have been allowed to return, officials said.

Winter Haven Police used police dogs to clear every inch of the park, police spokeswoman Jamie Brown said by phone. A statement from the department said bomb hoaxes are not "a joke," adding they will continue to investigate the case and bring charges.

Located between Tampa and Orlando in central Florida, the Legoland resort includes a 150-acre theme park with rides, restaurants, a water park and hotel. The park opened in October 2011 and the 152-room hotel opened in May last year.

Park officials said the campus was evacuated within 20 minutes. Officials declined to say how many people were in the park or staying at the hotel at the time of the evacuation.

(Reporting by Letitia Stein in Tampa, Fla.; Additional reporting by Curtis Skinner in San Francisco, Writing by Laila Kearney; Editing by Chris Reese)