Bomb disposal experts carried out a controlled explosion on a suspect package in the Monaco Grand Prix paddock on Thursday evening.
Security guards told Reuters a plastic container left near the entrance to the media centre was subsequently found to contain electrical cables.
The scare came with the paddock largely empty but parties in full swing on boats and at a floating Red Bull hospitality station moored next to the paddock turnstiles.
Friday is a rest day for Formula One and Thursday night is traditionally a time for paddock staff to let their hair down before the hard work of the weekend.
It is the second successive year that a bomb disposal unit had been called upon to attend to a package at the grand prix, a highlight of the social season attended by corporate CEOs, financiers and a sprinkling of billionaires.
(Editing by Ken Ferris; To query or comment on this story email email@example.com)