A snowstorm that pushed across London on Sunday brought Heathrow Airport, one of the busiest in the world, to a virtual halt as airlines canceled numerous flights and planes were stranded at gates.

Passengers described scenes of confusion and frustration. Some people boarded planes and waited for hours on the tarmac, only to have their flights canceled. Passengers waited for hours in lines that wound through the airport to speak with airline representatives. Many arriving flights were diverted.

Lee Hutchison said he and his girlfriend, Jo Wisbey, landed at Heathrow from New York on Sunday morning to discover that they had missed their connecting flight to Edinburgh, Scotland. Their airline, British Airways, booked them on another flight, which was canceled, and then two other flights, which were also canceled.

“Barely any flights went out, and the numbers of people needing rebooked grew and then would have to recycle people who kept having flights canceled,” Mr. Hutchison said in an interview.