TOKYO (AFP) - A Japanese man aged 73 sought to become the world's oldest person to swim across the country's Tsugaru Strait on Wednesday (Sept 7), braving treacherous currents and stinging jellyfish in his quest.

Toshio Tominaga's record bid will see him spend about a dozen hours swimming across the channel in northern Japan that is considered one of the world's most difficult because of strong and unpredictable currents, his supporters said.

The strait is only 19.5km wide at its narrowest point, but Tominaga will need to swim about 45km, attempting to go northward while battling currents moving eastward, support team member Masayuki Moriya said.

The septuagenarian began his swim at 5.28am local time Wednesday (4.28am Singapore), his supporters announced on Facebook.

Marathon swimmers usually attempt Tsugaru as part of their bid to complete the world's "Oceans Seven" long-distance swims, along with the English Channel, the Strait of Gibraltar and four others, according to the World Open Water Swimming Association (WOWSA).

In the past, swimmers have encountered sharks and fended off jellyfish and squid to complete the crossing, a feat first accomplished by US athlete David Yudovin in 1990.

In 2012, American woman Pat Gallant-Charette became the oldest person to swim across Tsugaru at 61, WOWSA founder Steven Munatones told AFP.

"The water is warm and if the conditions are good, there are no reasons why he should not be successful," Munatones said.

Last month, 18-year-old Japanese swimmer, Honoka Hasegawa, became the youngest person and the fastest woman to cross the strait.