A hoax caller threatened to "bomb" Blackpool Victoria Hospital, a senior police officer said.
Tactical operations chief inspector for Blackpool, Fylde, Wyre, Lancashire and Morecambe, Hassan Khan, said the malicious threat was not "clever or funny".
He said a man was arrested in connection with the calls in the early hours on Thursday.
The large hospital, in Whinney Heys Road, has 767 beds and employs more than 7,000 workers, making it one of the town's bigger employers.
It treats thousands of patients every day.
Nobody there could be reached for an immediate comment this morning, and it was not known whether the hoax call had any impact on services there.