The affected passengers required urgent medical assistance following the incident, News.Az reports, citing The Sun.
The BA603 flight, carrying 142 passengers, requested the landing at Bucharest Henri Coanda International Airport at 5.50pm local time.
It touched down soon after at 6.14pm and medical crews quickly boarded the plane to attend to the four that had fallen ill.
The other travellers were also evacuated while an emergency response team attended the scene.
Romania's Ministry of Health have since said in a statement that the “presence of smoke was confirmed” immediately after the plane landed.
The ministry added: “Four people are in poor health, possibly being smoke-intoxicated, and are receiving medical assistance on site.”
It is yet to confirmed if the four affected were cabin crew or passengers on the flight, but has assured that more details will follow.
On the British Airways website, the flight’s status currently says diverted.
A message also reads: “We’re very sorry, this flight scheduled from Istanbul to London, has been diverted to Bucharest.”
A BA spokesperson said: “Our crew made the decision to divert as a precaution due to a suspected technical issue.
“The aircraft landed safely and customers disembarked as normal,’ a spokesperson said.
“We’re sorry to our customers for the disruption to their journeys and our teams are working to get them on their way again as quickly as possible.”
