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".

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A man waits for a train in his underwear in the New York subwayTimothy A Clary/AFP
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A man looks at a woman standing on a New York subway platform in her underwearCarlo Allegri/Reuters
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Commuters dressed for New York winter weather look at a less sensibly dressed man in New YorkCarlo Allegri/Reuters
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People take photos of a woman taking part in the No Pants Subway Ride in the Manhattan borough of New YorkCarlo Allegri/Reuters
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Amused commuters in London look at a man in his pantsLeon Neal/AFP
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Participants in the annual "No Trousers On The Tube Day" head down to platform level in a station in LondonLeon Neal/AFP
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A woman takes a photograph of people taking part in the annual trouserless eventLeon Neal/AFP
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People travel in a London Tube carriage in their underwearLeon Neal/AFP
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A man wearing no trousers waits for a train during the No Pants Subway Ride in Mexico CityEdgard Garrido/Reuters
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Pantsless passengers wait on a platform in Mexico CityEdgard Garrido/Reuters
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People take part in the No Pants Subway Ride in BerlinHannibal Hanschke/Reuters
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People sit on a train in Berlin in their underwearHannibal Hanschke/Reuters
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A participant in the No Pants Subway Ride DC waits for a train at a station in Washington, DCMandel Ngan/AFP
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A man taking part in the No Pants Subway Ride DC lifts a fellow participant while waiting for a train at the Gallery Place - Chinatown station in Washington, DCMandel Ngan/AFP
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A passenger not wearing any pants waits for a subway train in PragueDavid W Cerny/Reuters
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Commuters look at people travelling on a train in their underwear during the No Pants Subway Ride in PragueDavid W Cerny/Reuters
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A man poses for photos during the annual No Pants Light Rail Ride in SeattleJason Redmond/Reuters
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Two men in their underwear wait to board a train in SeattleJason Redmond/Reuters