A pop star with ageing Japanese boy band SMAP has been arrested for public indecency, police said, amid reports he was naked and drunk in a central Tokyo park.

Tsuyoshi Kusanagi, 34, was arrested early in the morning near the Roppongi nightclub district after a local resident alerted police.

"We are still interviewing him here and cannot give any further details," said a spokesman for the Tokyo metropolitan police department.

Television networks reported the arrest by flashing bulletins usually reserved for earthquakes and other major events.

Public broadcaster NHK placed a breaking news headline over its live footage of a parliamentary session on Japan's measures to fight Somali pirates.

"What's wrong with being naked?" Kusanagi reportedly yelled at a police officer who approached him.

Boy band SMAP gained fame from the early 1990s and became hugely popular in Japan and elsewhere in Asia with a string of chart-topping hits.

Its members have used their fame to get roles in television dramas and movies, and Kusanagi has starred in films and featured in many commercials.

In South Korea, he is better known as "Cho Nan Kang" and liked for his good command of the Korean language.

SMAP, one of many successful pop groups formed by Japanese talent agency Johnny and Associates, is an acronym for "Sports Music Assemble People."