Hundreds of people in 54 cities around the world stripped down to their underwear on public transport for the annual No Pants Subway Ride.

The idea is for participants to maintain a nonchalant air, chatting with fellow passengers, listening to music, reading newspapers, while keeping a straight face as if all were perfectly normal.

The No Pants Subway Ride began in 2002 in New York with only seven participants and has grown into a global phenomenon. Organisers call it "an international celebration of silliness".