A man is lucky to be alive after climbing into a crocodile enclosure at a wildlife park in Broome in the far north of Western Australia last night.

Police say the man climbed the fence of the wildlife park and tried to jump on the back of a five-metre male saltwater crocodile after being thrown out of a local tavern for being drunk.

Sergeant Roger Haynes says the 36-year-old was bitten on the leg before managing to escape.

"For some reason he's made a decision to climb the fence into the crocodile park, where an almost five-metre male crocodile was living," he said.

"He appears to have wanted to touch that crocodile and sit on its back, and the crocodile has taken offence to that and bitten him on the right leg.

"He's absolutely lucky to be alive, this is a large male saltwater crocodile, who aren't renowned for letting people escape once they've got hold of them."

The owner of the park, environmentalist Malcolm Douglas, says the crocodile named Fatso is one of his largest reptiles and could crush a man in one bite.

But he says last night's cooler weather made Fatso more lethargic than usual.

"Once the temperature drops down their reflexes slow down because they are cold-blooded," he said.

"The fact that it was a cool night is probably what saved his life."

The man is undergoing surgery for severe lacerations to his leg at the Broome Regional Hospital.

Police say Mr Douglas does not want to press charges.