Daryl Evans and Kerry Thomas had been anchored and fishing for an hour at a spot known as The Barge, about 1.30pm, when the 3-metre shark came up under the boat in a berley trail.

"My first thought was 'We need a bigger boat'," Mr Evans said.

"It circled the boat about six times, from about 10 to 15 metres away until he was about 1.5 metres away."

The shark returned about 20 minutes later and circled the boat about 3-metres below the surface.

The men warned a nearby houseboat and swimmers in Swansea Channel.