Smoke billowing from Metro rail cars stopped at the Reagan National Airport station just before 11 a.m. Sunday delayed trains and caused a traffic snarl as emergency vehicles competed with people dropping off passengers on one of the busiest travel days of the year.

There were no reports of injuries, and Metro spokesmen were not immediately available to explain the circumstances. The transit agency initially posted on Twitter that riders on its Blue and Yellow lines should expect delays resulting from a “train malfunction” at National. By 11:20, the agency tweeted, normal service on the Blue and Yellow lines had resumed.

According to a Washington Post reporter who was dropping off passengers at the airport, smoke appeared to be coming from several rail cars at one end of the station and flames could be seen near the wheels. He said he smelled burning rubber.