A Cornwall fisherman is claiming that a species of shark blamed for countless attacks on humans rammed his boat.

The lifelong sailor believes the shark was an oceanic whitetip, a species that usually inhabits warmer and deeper waters.

He claims the 2 metre (7ft) long predator "zigzagged" towards his vessel and "slammed into it" before circling a second boat.

The 60-year-old mackerel fisherman, who asked not to be named, reported the sighting to the harbourmaster's office in St Ives, north Cornwall. He said he was "interested" when the shark began heading towards his boat. "I stood up to have a good look at it. As I was looking over the side of the boat, it just slammed into it.

"Then its head came out of the water by about a foot. It was that close to the boat that it slammed the side of the boat with its body and tail. It came as a bit of a shock. It was aggressive and we don't tend to have aggressive sharks in these waters."

He is certain it was not a porbeagle shark, often seen off the Cornish coast. "I have been fishing in these waters all my life and I have seen all sorts, but I have never had a shark ram my boat," he said. "This was an aggressive shark. I was in a 16ft [5 metre] boat, but if I had been in a kayak it could have easily had a bite at my legs."

He returned to port after the encounter and 10 minutes later two fisherman on board a second boat watched as a shark, believed to be the same one, circled them. One said: "I am 100% sure it was an oceanic whitetip. The water was crystal clear and we had a perfect view. It was pretty scary."

Richard Peirce, chairman of the Shark Trust, which promotes conservation and study of the creatures, was cautious about the sightings. He said: "It is always exciting and interesting to get sighting reports of what may be new species to our waters. Elements of the description we have heard are consistent with oceanic whitetips, although to date there have been no confirmed reports of oceanics in UK waters."

A spokesman for the harbourmaster in St Ives said he was not "100% sure" if the shark was an oceanic whitetip. The species has been blamed for many attacks on victims of shipwrecks and plane crashes at sea over the years. The spokesman said people should not blow the reports "out of all proportion".

The Western Morning News reported the sightings, saying: "A man-eating shark is feared to be prowling the waters off west Cornwall after two separate sightings of the predator considered the most dangerous of its species."

Shark sightings off Cornwall are generally treated with caution. In 2007 a video of a great white shark, supposedly taken off Cornwall, created excitement and fear before it was revealed that it had actually been filmed in South Africa. A Newquay nightclub bouncer had sent it into a local newspaper for a joke and been amazed when it made headlines around the world.

The oceanic whitetip is commonly found far further south in deeper waters away from the coast, with Portugal being the usual northernmost reach of its habitat. It is one of the species suspected of being behind attacks on people off Sharm el-Sheikh in Egypt.