Tokyo, Jun 5 (IANS): A French swimmer has set off from Japan aiming to become the first person to swim across the Pacific Ocean.

Ben Lecomte, 51, will swim for eight hours a day for more than six months as he heads towards the US west coast, BBC reported on Tuesday.

He faces dangers including sharks, storms, swarms of jellyfish, and extremely low water temperatures.

He is hoping to raise awareness for climate change, and a team of scientists will conduct research during the 9,000 km swim.

They will study plastic debris, the effect of extreme exercise on the heart and examine how the Fukushima nuclear disaster has affected the ocean.

Lecomte, who lives in the US, has been preparing with hours of open water swimming every day. He has also practiced "visualisation and dissociation" exercises to ensure he is mentally ready.

"The mental part is much more important than the physical," he said. "You have to make sure you always think about something positive."

"When you don't have anything to occupy your mind it goes into kind of a spiral, and that's when trouble starts," he says.

Preparations for the trip have taken more than six years, but Lecomte has been targeting the challenge for much longer.

In 1998, he made the first known solo trans-Atlantic swim covering 6,400 km in 73 days. When he finally reached dry land in France, his first words were "never again", but he was soon looking for a new challenge.