A US sailor has suffered serious injuries after jumping from the 10th floor balcony of a hotel into a swimming pool in Perth.

Police say the 22-year-old suffered a broken leg and internal injuries in the incident at the Parmelia Hilton about 1:00am.

He is undergoing surgery in Royal Perth Hospital.

Police said they were called to an incident involving a man and a woman from USS Carl Vinson, currently off Perth after a stint in the Middle East.

It is believed both were involved in an altercation before the man jumped from the balcony.

Police said both were believed to be heavily intoxicated.

The small pool is outdoors on the second floor of the hotel, next to the gym.

It is about 20 metres long and has a depth of 1.1 metres at the shallow end, dropping to 2.2 metres at the other end.

It is understood he landed in the shallow end of the pool, with police estimating he landed in 1.3 metres of water.

A senior police spokesman told the ABC it was an extremely dangerous stunt and "a sober person wouldn't do it".

A hotel guest, Malcolm, whose room overlooked the pool, said he heard the man crying out for help.

"I just heard his screaming and he sounded intoxicated," he said.

"I'm very surprised he attempted it.

"I thought he was lucky to make the water, to be quite honest with you. He's lucky to be alive."

Another guest said she thought it was amazing he survived the jump.

Details of the incident have been handed to the US Navy for an investigation.