Several aircraft were reportedly forced to abort landing on the London airport's southern 27R runway. Elsewhere fire appliances were seen escorting a British Airways Airbus A350-1041, which was flying from Dubai.
Conflicting reports claimed the problems were caused by a fox on the runway while others blamed it on a possible tailstrike or bird strike when landing.
Flightradar, which tracks the movement of planes, showed that several planes were repeatedly circling the airport apparently unable to land.
Social media was quickly flooded with some travellers claiming that planes had been redirected or were forced to circle before they landed.
mmleggat added: "BA plane surrounded by police and blue lights. Anyone know why? We're in T5."
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Others disputed the claim that a fox caused the chaos, insisting it was an issue with a plane.
Steve R68 wrote: "I've been watching Big Jet TV live stream from Heathrow and the fox DID NOT disrupt any flights at Heathrow.
"From what I heard a British Airways A350-1000 may have suffered a tail strike upon landing, it did a go around but landed safely.
"A runway inspection delayed arrivals."
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The chaos could now spark travel delays for hundreds of passengers who were scheduled to arrive and depart from Heathrow today.
It is one of the world's busiest airports and hosts hundreds of transit flights every day.
In pre-Covid times a plane was said to take off and land on one of its runways every 90 seconds.
As many wondered what was happening, Heathrow Noise tweeted: "Good afternoon, due to circumstances beyond our control we will switch our runways at 15:30, landing on the northern runway 27R and taking off from the southern runway 27L."
Express.co.uk has contacted the airport for comment.