According to Airlive news portal, "an aircraft is blocking runway 27R at London Heathrow". The Airport stated later, it was operating as normal; however, there has not been official information about the causes of the blockage.
"For a matter of minutes, one of the runways was out of service as an aircraft was towed from the taxiway. Heathrow is now operating as normal", a spokesperson said in a statement.
Several flights have been re-directed to other airports due to the incident.