Tokyo's Tsukiji fish market, the world's largest and one of the Japanese capital's most popular tourist sites, has caught fire amid government plans to relocate the popular shopping area.

Dozens of firefighters with some 30 fire trucks were on the scene battling the blaze which broke out just before 5:00 p.m. local time (0800 GMT) on Thursday, media said.

Efforts to extinguish the flames were hampered by the area's narrow streets and tight-knit buildings.

However, there were no immediate reports of injuries or people trapped.

The fire was in Tsukiji's "outer" market - an area packed with informal restaurants where tourists can tuck into fresh seafood plates and sushi.

Media reports said it spread to four buildings covering some 200 square meters of area.

A Japanese firefighter speaks to his colleagues with a speaker as they try to extinguish a fire at Tokyo's Tsukiji fish market on August 3, 2017. (Photo by AFP)

The Tsukiji "inner" market, where most seafood wholesalers are located and tuna auctions are carried out at dawn, was not affected by the blaze.

In June, Tokyo's governor Yuriko Koike announced a plan to move Tsukiji from its current location on some of the city's most prime real estate to a man-made island which critics say has contaminated soil.

Tsukiji draws tens of thousands of visitors a year to its warren of stalls laden with exotic species of fish, huge tuna and fresh sushi, part of a tourism boom that is a key part of Prime Minister Shinzo Abe's economic plan.

But Tokyo's governor said the 80-year-old market's age and vulnerability to a big earthquake meant it had to be rebuilt.