BOISE (Idaho) (REUTERS) - A moderate earthquake rattled a broad swathe of Idaho early Saturday, damaging property and causing power outages near its epicentre in Challis, a city that has endured hundreds of slight to moderate temblors over the past 10 months, authorities said.

The latest, measured at a magnitude of 4.9, was centred about 6.5km from Challis in the state's central mountains, but was felt as far away as Boise, a 305km drive to the south-west, the US Geological Survey said.

The quake caused rockslides, damaged homes and knocked out power around Custer County, local officials said.

Challis Mayor Mark Lupher said he was not in the area when the quake struck but that authorities have told him by telephone that there were no known injuries.

Several people living close to the epicenter reported property damage such as cracks in the walls of their homes, he said.

The latest in a string to rattle the area, the quake was more powerful than recent temblors, including a 2.9 magnitude quake on Dec 29, the USGS and Challis Messenger weekly newspaper said.

Scientists have been trying to determine whether the swarm of quakes, which began in March 2014, have been caused by a known fault thought to be dormant, or the result of an unknown fault.

The earthquakes have been centred near where Idaho's most powerful known quake, measured at 6.9, killed two children in 1983.

Idaho sits at the centre of a seismic belt that runs from northwestern Montana to southern Nevada and contains thousands of faults in the Earth's crust.

Scientists have said they do not believe the smaller quakes were leading to a larger event in the area.