Japan's tsunami-hit Fukushima region has kicked off a thousand-year-old horse festival, with riders in samurai armour defying an ongoing nuclear crisis to take to the streets and vow recovery.

The "Soma Namaoi", or wild horse chase, featured some 80 horses with riders in full samurai armour, and was dedicated this year to praying for those killed in the March disasters and for the reconstruction of local communities.

Locals marched through city streets just outside the 20-kilometre (12-mile) exclusion zone where nuclear workers are still battling to cool overheated reactors at a stricken atomic plant.

Michitane Soma, a direct descendant of the Soma clan which once governed the area, addressed the riders, each of whom carried a black mourning badge.

"Believe in the strength of the tradition of Soma Nomaoi," the 36-year-old said tearfully.

"March on and pray for the swift reconstruction of eastern Japan."

The three-day festival originates from secret military exercises held by 10th-century samurai warriors under the Soma clan, using horses as mock enemy soldiers.

The festival organisers had considered cancelling this year's event after many local residents were killed in the March 11 tsunami and earthquake, which left about 22,000 people dead or missing in total.

Other residents were forced to evacuate their homes, while many horses were also killed in the twin disasters.

But organisers decided to go ahead with the festival on a reduced scale from previous years, when the horses numbered 500.

And it took a more sombre tone than usual. Horse races with armoured riders were cancelled, as were the usual competitions to catch flags shot into the air with fireworks.