Dozens of people fled from a rural area bordering Norway's third largest city on Sunday because of a massive landslide but no casualties have been reported, police said.

"We have evacuated many farms," regional police operation leader Tore Kyllo told AFP after the landslide struck just south of Trondheim in central Norway.

The river of muddy black sludge stretching about a kilometre (over half a mile) was moving through the area and geologists have been sent up in a helicopter to evaluate the danger, Kyllo said.

Meteorologists said unusually warm December weather may have contributed to the landslide, with media speculating that a violent storm across Scandinavia late last month, which dumped massive amounts of rain on Trondheim, may have been the trigger.

"Most people have got out in their own cars or have been bussed out," Kyllo said. "I think a helicopter was used at one farm to help the evacuation process."

No one has been reported missing and no houses or farms have so far been swept away by the sea of mud, he said, but he added that "the edge of the landslide is unfortunately approaching a farm" and that the evacuation area might have to be widened.

The affected area is on a rural peninsula and there is no danger the landslide could affect the densely populated centre of the city of Trondheim itself, which is home to nearly 200,000 people.

Rune Petter Vikan, whose farm is located about 500 metres (yards) from the edge of the landslide, told public broadcaster NRK that he was not worried that his farm would be hit.

"Not really, but we don't have any control over what is happening. It's not a fun situation, since more can suddenly go. We just don't know," he said.

A reporter with the local Addresseavisen said families in the area were jumping into their cars with a few possessions and speeding off.

"They obviously had only had time to grab a few things in the rush to get out. I saw one family with small kids just grabbing a pack of diapers as they left," Haavard Jensen told the paper.