US Edition The pilot pressed the wrong button which triggered an automated voice message that was broadcast throughout the plane, The Sun claimed.
It said: "This is an emergency announcement. We may shortly need to make an emergency landing on water."
The flight was travelling from Heathrow to Hong Kong and the warning was issued as the aircraft flew over the North Sea.
When cabin crew realised the ran down the aisles reassuring the 275 passengers that it was a mistake.
The airline has apologised for "undue distress".
Last year panic broke out on an Aer Lingus flight from Dublin to Paris when an emergency landing announcement was played by mistake just 20 minutes into the journey.
A first announcement was made in English telling passengers to return to their seats due to turbulence.
A second warning was then played warning of an emergency landing in French causing panic amongst the French passengers.
An airline spokesman said: "There was a malfunction of the public address system and we apologise to our passengers.
"This sort of thing happens very rarely."