Professional distance swimmer Ben Lecomte has set off from Japan to San Francisco in an attempt to become the first person to swim across the Pacific Ocean.
Lecomte left at 8am local time today from Choshi, which is north-east of Tokyo in neighbouring Chiba prefecture, spokesman Alexandre Borreil said.
He is expected to swim eight hours daily on a journey that could take six to eight months and will cover about 8,000 kilometres (5,000 miles).
"For the moment we know he left and everything went well," Mr Borreil said.
Lecomte completed a similar swim across the Atlantic in 1998, organisers said.
He is doing this swim to raise awareness about the health of the world's oceans and the threat of pollution.
Scientific teams accompanying Lecomte will collect more than 1,000 water samples and study plastic pollution, mammal migration and the effect of extreme endurance events on the human body.
- Digital Desk and PA