An American fisherman in his 50s who was swallowed by a giant humpback whale has miraculously survived.

Michael Packard, 56, of Cape Cod, Massachusetts, USA, was sucked into the mouth of a humpback whale while out hunting for lobsters on the 11th local time.

According to the Associated Press, Packard went out on a boat off Cape Cod to check lobster traps.

Packard, a crayfish diver for 40 years, jumped off a boat while wearing scuba gear.

After diving into the sea, he suddenly felt a huge shock at a depth of 10m and the whole area became dark.

Packard initially thought he had been attacked by a shark.

However, fumbling around with his hands confirmed that it had no sharp teeth, and soon realized that it had been swallowed by a humpback whale.

Packard remained trapped in the whale's mouth for 30 to 40 seconds.

"The whale tried to swallow me," he said. "I thought I was going to die."

But the whale suddenly rose to the surface and shook its head violently, spitting the Packard back into the air.

He miraculously came out of the whale's mouth and was rescued by colleagues on a boat and taken to hospital.

The medical staff thought he had broken his leg bone, but the examination revealed no major injuries other than a bruise, and he was discharged a few hours later.

"He's so lucky and blessed," said Packard's mother, Anne, "it's unbelievable."

Dr Charles Mayo of the Provincetown Coastal Research Center in Cape Cod said swallowing humans is very rare because humpback whales are not aggressive animals. 

(Photo = Twitter post capture, Yonhap News)