Rescue workers airlifted residents out of isolated villages and sifted through wreckage for earthquake survivors Sunday, a day after a series of strong temblors hit northwest Japan, killing at least 23 people and injuring more than 2,000..

Dozens of quakes and tremors Saturday evening, the first and strongest measuring magnitude 6.8, rocked a largely rural area around the town of Ojiya, about 160 miles northwest of Tokyo. As smaller aftershocks continued to jolt the area Sunday, Japan's Self-Defense Forces launched rescue operations, helicoptering out dozens of people from villages cut off by damaged roads and bridges.

Early Monday, an earthquake with a magnitude of 5.6 shook the same area of northern Japan, according to Japan's meteorological agency. There were no immediate reports of injuries or damage.

Tens of thousands of people spent a second night in emergency shelters on Sunday, and more than 100,000 homes remained without power. At least five people were still reported missing. The fatalities ranged from an infant boy to people in their seventies, officials said.

Hospitals in the region appeared overwhelmed. Television broadcasts showed patients being treated in waiting rooms.

Damaged and blocked roads continued to impede damage assessments. The National Policy Agency said at least 76 homes had completely or partially collapsed and reported extensive damage to infrastructure.

The quake was the deadliest in Japan since a massive tremor struck the western port city of Kobe in January 1995, killing more than 6,000 people.

Prime Minister Junichiro Koizumi dispatched disaster officials to the affected areas Sunday and said the government would promptly earmark funds for a major rebuilding effort.

"The government will do its utmost to coordinate and promote relief measures for the disaster," Koizumi's chief cabinet secretary, Hiroyuki Hosoda, said at a news conference.

The series of quakes began at 5:56 p.m. Saturday. The force of the first one derailed two cars of a bullet train heading north from Tokyo to Niigata. No one was injured in the accident, the first derailment of Japan's trademark high-speed trains since they began running in 1964. East Japan Railway Co. told Japan's Kyodo news service Sunday that it would take several weeks to repair the section of track damaged by the quake.

Sewage and water mains burst, and gas and telephone service was down in much of the affected region. Officials in the area were struggling to restore running water to 36 cities, towns and villages in Niigata prefecture on the Sea of Japan, according to Kyodo.

"I was really hoping to see the dawn, as we had no lights due to the blackout," Shoji Takizawa, 68, of the town of Toka, near Ojiya, told Kyodo. Takizawa said he spent the night in a car with his wife and son. Many residents in the region also used vehicles for shelter.

The earthquakes hit just days after Japan's deadliest typhoon in more than a decade left 79 dead and a dozen others missing. The typhoon had soaked the region hit by the quake, which helped cause at least 37 mudslides, officials said.

Japan lies in one of the most earthquake-prone regions in the world, accounting for about 20 percent of quakes magnitude 6 or greater.

Vehicles lie abandoned on a stretch of road in the northwestern Japanese city of Nagaoka after it collapsed during one of several earthquakes on Saturday.A warehouse in the northwestern village of Yamakoshi was among many structures destroyed or damaged by the tremors, which continued Monday.