Terrified passengers can be heard screaming and crying in video footage of the moment thick smoke poured into the cabin of a Ryanair plane mid-flight.
Smoke began to flood the packed cabin just moments after the Boeing 737-800 took off from the Romanian capital of Bucharest, climbing thousands of feet into the air.
A woman can be heard crying in panic in footage filmed on board the aircraft, while a man can be seen grappling with an overhead compartment in an apparent attempt to release an oxygen mask.
None of the other overhead compartments appear to be open.
The flight to London Stansted was grounded just minutes into the journey after the pilot declared an emergency and returned to Otopeni airport.
According to Ryanair, it is believed the smoke may have been caused by de-icing fluid entering the air conditioning system.
The flight was reportedly originally scheduled for 6.40am but had already been delayed because of an issue with the first plane.
The 169 passengers and four crew members then boarded a replacement plane, which took off about four hours later but returned to the airport after filling with smoke.
A third plane was then prepared, however some passengers reportedly refused to travel with the airline because of their experience.
A spokeswoman told MailOnline the replacement aircraft had been de-iced before it set off for London.
An investigation into the cause of the smoke is still ongoing.
