TOKYO, July 23, 2008 (AFP) - A powerful earthquake shook northern Japan early Thursday, injuring at least 90 people as its force shattered windows and set off fires in an area hit by a deadly tremor just a month ago.

The earthquake, measuring 6.8 on the Richter scale, struck the north of the main Japanese island of Honshu as most people were asleep and cut off power to around 10,000 homes, officials said.

"I've never felt such a big tremor in my life," said Hirokatsu Hashimoto, an official in the northern city of Hachinohe.

Police said at least 90 people had been taken to hospital with injuries after the quake struck at 0:26 am (1526 GMT Wednesday) in Iwate prefecture.

The tremor was centred 108 kilometres (67 miles) underground, the Japan Meteorological Agency said.

Fire engines and ambulances rushed through Hachinohe with sirens blaring after fires broke out, but officials later said the blazes had all been extinguished.

"I woke up with a big shock. I was wondering what the hell was going on," said Takashi Kato, an official of Morioka, a city close to the epicentre.

"I haven't received any immediate report of damage, but part of the city hall ceiling was damaged," Kato said.

In Tokyo, Japanese Prime Minister Yasuo Fukuda said he had ordered officials to "do their best" to rescue any people trapped by the earthquake.

The government set up an emergency office to handle the impact of the quake, which was strong enough to shake buildings in the heart of the capital some 500 kilometres (300 miles) to the south.

"It was shaking a little at first and then suddenly we felt a big rolling feeling," said Ryuichi Takedaka, an official at the Hirono town office near the epicentre.

"It continued rolling for a while," he told public broadcaster NHK. "I walked to the office and saw glass windows shattered at some houses along the way."

Television footage showed office floors covered in paper that had been shaken from the desks.

"It was a strong quake but I didn't see things fall from the shelves," said Yasuko Tomabechi, a rice farmer in the northern city of Towada.

The quake struck near the epicentre of a powerful June 14 earthquake that measured 7.2 on the Richter scale, killed at least 13 people and left 10 others missing.

Japan endures some 20 percent of the world's powerful earthquakes.

The area of the earthquake lies near Rokkasho, the hub of Japan's nuclear power industry and site of a controversial plant that reprocesses spent fuel.

An earthquake last year caused a small leak in the world's largest nuclear power plant in Niigata prefecture northwest of Tokyo.