A number of flights to UK airports have been diverted after "smoke smells" were reported on board.
EasyJet said four of its flights were diverted due to "atmospheric circumstances".
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A British Airways spokeswoman said the carrier has had "some reports of smells on board" but the aircraft continued to their destinations.
Liverpool John Lennon Airport stated that "atmospheric conditions" are believed to be causing flights to divert.
An easyJet spokeswoman said: "EasyJet can confirm that four of its flights flying in the west of the UK have reported smoke smells in the cockpit today, believed to be linked to atmospheric circumstances due to storm Ophelia.
"Two flights returned shortly after take-off and two flights requested an expedited landing as a precaution only.
"We understand other airlines have experienced similar events and we continue to liaise with the Met Office as to the likely cause.
"The safety and welfare of our passengers and crew is easyJet's highest priority. We would like to apologise for any inconvenience experienced by the diversions."
BA said in a statement: "The safety of our customers and crew is always our priority.
"Our flights have been operating and landing normally, but we have been liaising with the Met Office about atmospheric conditions."