Story highlights Woman and her children found dead in their snow-trapped car

Four other people in Hokkaido prefecture froze to death during weekend

High-speed train derailed in blizzard conditions in Akita prefecture

Heavy snow in northern Japan claimed the lives of eight people over the weekend, while a blizzard forced a high-speed bullet train to derail.

In one incident, a woman and her three children were found dead on Saturday after becoming trapped in their car in Nakashibetsu, a town in eastern Hokkaido prefecture, police told CNN.

Authorities believe they died of carbon monoxide poisoning as the car's engine was left running and filled with exhaust fumes. The vehicle's exhaust pipe and windows were buried under snow.

A 23-year-old woman, also from Nakashibetsu, died Sunday after she was found collapsed on farmland near the town. Police said she had abandoned her car, which was found a few hundred meters away.

Elsewhere in the region, a 53-year-old man and his nine-year-old daughter were discovered unconscious after being buried in snow on farmland near Yubetsu in Monbetsu district. The father was pronounced dead at hospital, but his daughter is now conscious and does not have any life-threatening injuries, police said.

The two went missing after leaving their home Saturday afternoon in a truck to visit a friend of the father. Police and rescue workers found the truck on a road Saturday evening and the man and his daughter Sunday morning. According to local media, the father had covered his daughter with his body to try to warm her under heavy snow.

The bodies of two other men -- ages 74 and 54 -- were also found outside Sunday. They are believed to have gotten lost after leaving their snow-trapped cars, and police say the elder man froze to death; the other's man's death is under investigation.

Meanwhile, a six-car bullet train en route from Tokyo to Akita on the high-speed Akita Shinkansen line derailed on Saturday afternoon after the front wheels of the train's first car left the track in blizzard conditions near Daisen in Akita prefecture. Nobody on board was injured, and the service resumed on Monday, a spokesperson for operator JR East told CNN.

Local media reports said the train remained in the same spot for six hours in snowy weather with 130 passengers stranded inside.

Investigators from JR East are looking into the cause of the incident.