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.
UPDATE: London Heathrow resuming movements after #BA162 (Airbus A350-1000 G-XWBD) stopped on Rwy 27R with hydraulic fluid spill after landing at 0940UTC from Tel Aviv. Some diversions to Gatwick & Stansted.— Airport Webcams (@AirportWebcams) February 19, 2020
Info via passenger at LHR @twiterrs | Photo via @richd777 pic.twitter.com/aIhTZEq9MI
Several flights have been re-directed to other airports due to the incident.