Two South Australian fishermen landed a surprise catch when a 3.2-metre thresher shark jumped into their small dinghy during a weekend fishing trip.

Fishing buddies Peter Feast and Jim Ewing were out chasing snapper and whiting at sunrise on Saturday, around one kilometre offshore at Green Point, near Port Macdonnell, when something big took Mr Feast's rod.

"It started screaming," Mr Ewing told the ABC. "He grabbed it and he let it run and it came away. He said 'thank God for that, it must have been an eagle ray or something like that'."

Mr Ewing said Mr Feast was fiddling with his rod at the stern of the 4.3-metre dinghy when he spotted a disturbance in the water to his right.

"Next thing you know, this thresher shark jumped completely clear of the water and splashed down," he said.

With both the men's attention now on the water, Mr Ewing said the shark performed the same stunt twice more.

"We have never seen anything like this before in our lives.

"The next thing I could see was this head and mouth coming over his shoulder and it crashed into his shoulder as it came through.

"It landed flat, bang on the deck of the boat between the two of us."

Shark nearly dwarfs boat

The thresher shark, of which one third is an enormously powerful tail, almost dwarfed the dinghy, said the men.

The flabbergasted Mr Ewing, facing the shark's teeth, said he jammed his boots on its head, trapping it against a fishing box and the side of the boat.

The shark almost dwarfed the small dinghy, the men said. ( Supplied: Peter Feast )

"Meanwhile the tail is thrashing around and Peter is trying to duck the tail. It smashed one of his rods," Mr Ewing said.

"The power that tail can generate in order for a great big shark like that to totally clear the ocean, man, there is some power in it."

The shark eventually settled down, allowing the men to tie a rope around the thrashing tail and anchor it to the seat of the boat.

"Then we had it under semi-control," he laughed. "Well, as much control as you can have over a shark."

Mr Ewing said their thinking was that "if it starts thrashing and snapping and biting again, we were in big trouble".

Fearing the shark had been scared by a larger predator, they said abandoning ship was not an option.

"There is a shark called Old Joe, a big great white, that we've encountered there. It frequents the area," he said.

"We couldn't very well jump over the side."

Flake for breakfast

The hungry pair thought seriously about flake fillets for breakfast before deciding to let their surprise visitor go.

As it was too risky to try to lift the shark overboard they went back to shore.

"A couple of young guys on the beach helped us unload it and we got it into the water," Mr Ewing said.

"Unfortunately it thrashed a little bit but we couldn't get it going. I guess it had just been out of the water for too long.

"It was kind of tragic we couldn't get it back in the water and do the right thing."

The pair measured the shark and said it was 10-and-a-half feet, or 3.2 metres in length.

After heading back out to check their lobster pots, the pair returned to find the shark dead and decided to make use of it.

"We will be eating thresher shark fillets for the next month or two," said Mr Ewing.

The men were able to get the shark off the boat, but it did not survive. ( Supplied: Peter Feast )

Upon arriving home, Mr Ewing said he found numerous accounts on the internet about the sharks leaping into boats.

After the story was shared on ABC South East SA's Facebook page some queried the pair's story, but it has since been substantiated by other fishermen angling nearby.

"These guys were in the boat next door to us, we saw it," commented Ben Tremelling, while his fishing partner Luke Boneham remarked the pair were "kool (sic) as".

Fishing tales are renowned for getting bigger with each re-telling, but the pair swear their story is true.

"It certainly happened. Peter is a truthful guy, and I'm a pretty truthful guy," Mr Ewing said.