A kayaker has had a close call with a large shark in King George Sound in Albany, off Western Australia's southern coast.

Ian Watkins made a mayday call to nearby whale-watching vessels after a shark believed to be about four to five metres long took a keen interest in him.

Mr Watkins said he initially thought the shark was the wake of a nearby whale-watching vessel and then he realised it was a white pointer following him.

"This wave was coming behind me and I thought 'what the heck's that', and then I looked on and there's this massive fin, and I thought 'that's a serious shark'," he said.

"It pushed me from the left hand side and then it nudged me from the middle across the left hand side.

Ian Watkins was paddling his kayak when he was threatened by a white shark. ( ABC News: Kendall O'Connor )

"I was trying to stay upright and then it circled me for a while and I got on the radio and said 'emergency, emergency, emergency'."

Paul Guest was in his charter vessel about 600 metres away from the man when he received the emergency call.

"We've got a bit of a panicked call from somebody who said they were on a ski or sea kayak and said they had a white pointer swimming around them and they needed assistance, because it was bumping into them and giving them a bit of grief," Mr Guest said.

"Passengers at the back of the boat pointed to him so we turned around and headed to them at full speed.

"We backed off the revs as we got to him, so we didn't knock him off his ski, I thought that was something we didn't need to do."

Mr Watkins said he was not sure how big the shark was, but it was as big as his kayak.

"My kayak's 17-feet long, but I don't really know the length [of the shark], it was a bit murky. I was more interested in staying upright," he said.

"Then he kept circling me, it went from the right under the kayak, then from the left under the kayak …when it was coming under it was just really white it was massive and I thought 'holy … bloody hell'.

"I don't know whether it would have actually attacked me or whether it was just checking me out but it was definitely interested and didn't let me go."

Mr Guest said Mr Watkins was local, experienced and carried all the right safety gear, but he still would not personally be kayaking around that area.

"The guy said it was a great white and believed it was about the size of his ski; I know the skis are at least 5, 5.2 metres long, so if it was that big, it was a fair-sized shark," he said.

"I told the guy maybe you should get a bigger boat."