A British Airways flight on Monday made a U-turn back to the UK just an hour into its journey from London to Chicago, according to flight tracking data.

Flight BA295 declared an emergency mid-flight following a sudden and steep descent while flying over Ireland soon after take-off from London’s Heathrow Airport at 1150 am local time, according to flight tracking data.

The Boeing 777-200ER plane had a scheduled flight time of eight hours and 40 minutes to Chicago O'Hare International Airport (ORD).

However, about an hour after take-off, the aircraft had climbed to its cruising altitude of 37,000 feet when it appeared to encounter an issue and was squawking – the international aviation signal for a general emergency.

Flight-tracking data shows the aircraft initiated a rapid descent, dropping 28,000 feet to an altitude of 9,000 feet within minutes.

The nature of the emergency is not yet clear, and a statement from the airline is awaited.

(With inputs from PTI)