ICHINOSEKI, Japan (AFP) - Rescue teams searched under dense fog and rain Thursday for victims of a powerful earthquake in northern Japan that left more than 100 people injured, some of them seriously.

The 6.8 Richter-scale quake struck just after midnight on the mountainous northern tip of Japan's main island of Honshu, shattering windows and triggering landslides that blocked key roads on the Pacific coast.

Some 110 people were injured, according to a tally by public broadcaster NHK. Police said that 15 of them were in serious condition, some having broken bones as the quake threw them to the ground.

Military helicopters scoured the region famed for its blueberry fields and hot-spring resorts to find if anyone was trapped, but low visibility and light rain hampered the operations.

"I've never felt such a big earthquake before in my life," said Kenji Sasaki, a disaster official in the town of Hirono where the walls and ceilings of the municipal head office suffered cracks.

"I was asleep when I felt the jolt but for its entire duration I couldn't move," he told AFP.

Prime Minister Yasuo Fukuda also said he was startled by the quake, which was so powerful that it shook buildings in the capital some 500 kilometres (300 miles) to the south.

"I was just about to fall asleep. I think everyone else was alarmed as well," Fukuda told reporters.

"As a nation we will promptly take appropriate measures," Fukuda said.

"However, it appears that the area is now foggy so it's difficult to assess the situation by helicopters. We would like to clarify the situation as quickly as possible."

Japan, which lies at the crossing of four tectonic plates, experiences some 20 percent of the world's powerful earthquakes.

Just one month ago, an earthquake of 7.2 on the Richter scale hit the same area, leaving 23 people dead or missing.

Officials were thankful that, for the moment at least, there were no indications of deaths from the latest earthquake.

"We received many reports of injuries after the earthquake but we haven't heard of any cases yet this morning," said a fire department official in the city of Hachinohe where the quake was felt strongly.

He said that about 20 fire engines were patrolling the city streets in case of any fires or injuries. One fire broke out in the city after the earthquake but was put out within half an hour without causing casualties.

The earthquake was a relatively deep 120 kilometres (75 miles), meaning it was felt over a larger area, said Takashi Yokota, director of earthquake and tsunami monitoring at the Japan Meteorological Agency.

In Sendai, the biggest city in northern Japan, 40-year-old brick wholesaler Yasutoshi Hanei said that comic books poured off the shelves at the bookstore of one of his customers.

"It was like there was a grinding feeling coming from all sides," he said.

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