KURIHARA, Japan — Rescue squads and military helicopters raced to find 11 people missing after an earthquake in mountainous northern Japan sent hillsides crashing down Saturday, killing at least six and injuring more than 140.

The 7.2-magnitude quake triggered several major landslides, blocking roads and stranding about 100 bathers at a hot spring resort. Crews searching for the missing had to hike mountain trails and dig their way to the worst-hit areas.

"It was the worst quake I have ever felt," said Rinji Sato, whose grocery store in this town near the epicenter was a mess of shattered bottles and food thrown from shelves. "We were just lucky this didn't hit a big city."

Officials said at least 144 people were injured, a number that would surely have been higher if the quake had hit a more heavily populated area. Sato described the temblor as a sharp vertical jolt followed by a powerful sideways swaying.

"It was impossible to stay on your feet," he said.

The government responded quickly, mobilizing troops, police and fire department rescue teams to find and care for the injured and to recover the dead.

"Our most important task is to save as many lives as possible, and we are doing the best we can," Prime Minister Yasuo Fukuda said.

Access, however, was a major obstacle.

The quake — followed by more than 150 aftershocks — buckled roads, including one highway that was severed when a stretch of land collapsed, turning it into a sudden drop-off. Trains also were halted throughout most of the region while workers checked the safety of the tracks.

Hundreds of people in several isolated towns with disrupted roads were waiting for rescuers to arrive more than 12 hours after the quake.

"We're getting growing reports of damage, but we can't even get out there to assess the situation with roads closed off because of landslides," said city official Norio Sato in Kurihara, one of the worst-hit cities in northern Miyagi prefecture (state).

Seven people at Komanoyu hot springs were missing and believed buried after a landslide hit the resort, said another Kurihara city official, Katsuyuki Sato. Another 100 or so people were stranded but safe. Kurihara officials said four more were missing elsewhere, bringing the total missing to 11.

At a nuclear power plant in Fukushima, about 60 miles away, the jolt splashed a small amount of radioactive water from two pools storing spent fuel. Trade and Industry Ministry official Yoshinori Moriyama said there was no leakage outside the plant.

The Defense Ministry dispatched a dozen helicopters and patrol aircraft to the region to conduct flyovers and assess the extent of damage. The government also sent a CH-47 helicopter carrying Disaster Minister Shinya Izumi to the region.

The 8:43 a.m. quake was centered about 5 miles underground in the prefecture of Iwate. It was felt as far away as Tokyo, 250 miles to the southwest.

"It shook so violently that I couldn't stand still. I had to lean on the wall," said Masanori Oikawa, a city official in nearby Oshu who was at home when the quake struck. "When I rushed to the office, cabinets had been thrown onto the floor and things on the desks were scattered all over the place."

Electricity was cut to about 29,000 households and water to about 500 others, though services were mostly restored by Saturday night.

The dead included three construction workers who were on a hillside when the morning quake struck. The ground gave way beneath them, and they tumbled about 300 feet to their deaths in the avalanche. Twelve others at the site managed to dig themselves out of the landslide.

Another victim ran out of a building in fear and was hit by a passing truck.

Japan is one of the most earthquake-prone areas in the world. The most recent major quake in Japan killed more than 6,400 people in the city of Kobe in January 1995.