An Australian scientist on Wednesday said he had discovered what could be the world's rarest coral in the remote North Pacific Ocean.

The Pacific elkhorn coral was found during underwater surveys at Arno atoll, in the Marshall Islands, by coral researcher Dr Zoe Richards of the ARC Center of Excellence for Coral Reef Studies ( CoECRS).

The coral bears a close physical resemblance to the critically endangered and fast-vanishing elkhorn coral, or Acropora palmata, of the Atlantic Ocean. But genetic analysis has shown it to be a different species.

"When I first saw it, I was absolutely stunned. The huge colonies - five meters across and nearly two meters high with branches like an elk's antlers - were like nothing I'd seen before in the Pacific Ocean," Dr Richards said in a statement.

"So far I have only found this new population of coral to occur along a small stretch of reef at a single atoll in the Marshalls group.

"It grows in relatively shallow water along the exposed reef front and, so far, fewer than 200 colonies are known from that small area."

Richards said Pacific elkhorn colonies were by far the largest of all the Acropora colonies seen at Arno Atoll, indicating they were relatively old.

Whether the Pacific elkhorn is an entirely new species or not is subject to scientific debate.

Richards discovered that in 1898 a scientist described a coral from the island of Rotuma, near Fiji in the South Pacific whose description fits that of the Pacific elkhorn.

"Unfortunately at this stage, we do not have any genetic material to confirm whether or not it is the same species as the Pacific Elkhorn," he said.

According to Australian Associated Press, either way the discovery is good news. Acropora is the dominant genus of reef- building corals.

Leading coral geneticist Professor David Miller, of the CoECRS and James Cook University, said the discovery showed how much was left to learn about remote reefs of the North Pacific.