Update: The British Airways flight that was diverted en route from London to New York has safely landed at Heathrow after issuing an emergency alert.
Flight BA115 sent out a 7700 squawk this afternoon as it was flying over Ireland, changing course to return back to the capital.
The squawk was subsequently changed to 7213, which is thought to mean there was a mechanical problem with the Boeing 777-236.
One social media user, who appeared to be on board, claimed the pilot reported "fumes on the flight deck". He also praised the flight crew and pilots for their handling of the situation.
Pilot reported fumes on the flight deck #ba115 looks like we're de planing.— Lucas Chung (@Lkkchung) May 28, 2015
Kudos to #ba115 flight crew. Pilots landed perfectly on emergency O2— Lucas Chung (@Lkkchung) May 28, 2015
The plane turned back when it was over Ireland, and the diversion took less than an hour, landing just after 5pm. However the exact nature of the reason for diverting is still unknown.
British Airways is yet to comment on the situation.
After it had landed, the AirLive agency confirmed the problem was of a technical nature.