I was on a SQ B777, on an airbridge stand at SIN. Mid-way through boarding, the Captain announced "please will everyone deplane immediately". Wasnt an evac and the cabin crew rushed pax to the 2 open doors (First and Business) avoiding any closed doors. Obviously SQ had a mid procedure.
Interestingly the Capt then came into the terminal and told us he had a fire warning in the hold, which was why he asked us to leave immediately, but he didn't deem that to be urgent enough to evac. Turned out to be an aerosole but he couldn't have known that. After we reboarded 2 hours later, we taxiied to the runway and returned to stand due to an issue with the flaps, unsurprisingly a couple of pax then decided they wanted to get off the flight!