A SkyWest Airlines flight from Chicago has made an emergency landing in Buffalo, New York, after three passengers mysteriously lost consciousness.

The flight carrying 75 passengers left O'Hare Airport bound for Bradley in Connecticut, but was forced to land at Buffalo Niagara Airport.

The Federal Aviation Administration said the crew of the SkyWest Embraer E170 jet, operating as United Express, reported a possible pressurisation problem, but SkyWest spokeswoman Marissa Snow said maintenance staff found no indication of any issue with the aircraft and the airline was continuing to investigate.

It was reported earlier that only one passenger lost consciousness, but Ms Snow said medical staff confirmed that three lost consciousness. The passengers were evaluated and released with none needing hospital treatment, she said.