An RAF search-and-rescue team is searching Wytham Great Wood, near Eynsham, where a light aircraft was believed to have crashed earlier tonight.
The aircraft, with two people on board, was due to land at Oxford Airport, but the airfield lost contact.
An RAF helicopter was scrambled from Lee-on-Solent in Hampshire at 6.30pm to help in the search.
A police spokesman said: "We received a call to say Oxford Airport had lost contact with a plane that was due to come in.
"We are trying to find where the plane has gone, but no-one has found it yet."
Earlier, firefighters were sent to Oxford Airport in case the plane crash-landed at the airfield.
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