A Tasmanian abalone diver's 20-minute encounter with a great white shark has prompted a warning to all commercial divers to adopt new safety techniques.

Key points: A professional abalone diver collided with the huge shark when he pushed off from the seabed

A professional abalone diver collided with the huge shark when he pushed off from the seabed The diver had to lay face down flat on the seabed, hanging on to kelp, to maintain a low profile

The diver had to lay face down flat on the seabed, hanging on to kelp, to maintain a low profile New safety recommendations include divers having an underwater slate, an agreed signalling method, and shark deterrents

The Abalone Association of Tasmania has distributed an email to members telling how a diver had an encounter with a five-metre shark near Maatsuyker Island off Tasmania's South Coast.

Head of the association, Dean Lisson, said the diver — whose name has not been released — was working alone at depth of 14 metres, gathering the shellfish delicacy abalone when he was first buzzed by the great white shark.

Map Maatsuyker Island, off the south coast of Tasmania

"The diver first became aware of the great white when he pushed himself and his bag of abalone off the bottom and the shark collided with him from behind," Mr Lisson said.

According to Mr Lisson, the shark then charged at the diver for a second time at great speed.

Diver hid on ocean bottom

What followed was a 20-minute game of cat and mouse.

Abalone is a shellfish delicacy which is largely harvested by divers. ( ABC News )

"Instinctively, and with almost no time to react, the diver lay face down flat on the bottom and hung onto kelp to maintain his horizontal position and 'low profile' on the bottom," Mr Lisson said.

The diver was then repeatedly "bumped" from behind, in what he thought was an attempt by the shark to bite him.

According to the account sent to other members of the Tasmanian Abalone Association, the diver lost his bearings and without realising, swam into deeper water looking for a gutter to lay in.

Looking for the way to shore

When realising he was in about 18 metres of water, the diver stopped and tried to work out which direction the shore was.

He was approaching dangerous depths for diving where a decompression stop midwater is required before returning to the surface.

Mr Lisson said "understandably, it took all of his willpower not to make a dash for the surface".

Realising that something was amiss, the diver's deckhand on the boat above threw a dropline to the diver with an underwater slate attached.

"The diver wrote a message on the slate and pulled the dropline signalling the deckhand to retrieve it," Mr Lisson said.

"The message was for the deckhand to orient the vessel with its bow pointing to the nearest shoreline. In this manner, the diver was able to determine which way to swim."

Mr Lisson said the diver swam toward the shore and when in shallow water, with the vessel directly above him, was able to swim the short distance from the bottom to the diver's door on the vessel and quickly pull himself aboard.

The new safety recommendations include divers having an underwater slate with them, agreeing on a signalling method with the deckhand on the boat above, and for divers to use a shark deterrent such as a shark shield.