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One of Japan's largest organised crime gangs is reported to have split into rival factions, sparking fears of a turf battle.

Some key members of the Kobe Yamaguchi-gumi have left to form a splinter group in central Hyogo prefecture, Japanese media report.

One member said they were unhappy at the way their former gang chief was collecting money.

Police said they would be on alert for any possible violence.

The Yamaguchi-gumi gang is the largest of Japan's organised crime syndicates, known as the yakuza. Police say it has about 23,000 members.

Yakuza gangs have been part of Japanese society for a long time; there are believed to be about 60,000 members nationwide.

The gangs themselves are not illegal, although much of their earnings are gained illicitly through gambling, prostitution, drug trafficking and, increasingly, cyber-hacking.

The new group told reporters it would be called Ninkyo Daintai Yamaguchi-gumi and, although it would not have a boss, would be represented by Yoshinori Oda, 50, a former executive of the old gang.

The Kobe Yamaguchi-gumi gang was formed two years ago after powerful factions split away from the main Yamaguchi-gumi group.