The world's largest and most powerful particle accelerator and one of humankind's most ambitious scientific endeavours, the Large Hadron Collider (LHC), has been shut down — by a weasel.

The multi-billion-dollar project near Geneva in Switzerland, designed to smash sub-atomic particles at close to the speed of light, unexpectedly lost power a day ago, despite a series of sophisticated safeguards.

The small, furry culprit had chewed on a 66-kilovolt electrical transformer, according to a report by CERN, the LHC's operator.

But the critter was unable to weasel itself out of the hairy situation, and researchers found its fried body next to the gnawed electric cables.

It did not get into tunnels, just the electrical facilities at the site, CERN spokesman Arnaud Marsollier told the BBC.

He said it was not too surprising an animal had impacted equipment, given the facility was in the countryside.

It would take a few days to get the facility back to working order after the weasel's visit, Mr Marsollier said.

"Not the best week for LHC!" CERN's incident report said.