An Alaska Airlines flight bound from Chicago’s O’Hare Airport to Seattle made an unscheduled landing at the Minneapolis-St. Paul International Airport on Wednesday night after a foul odor sickened some passengers and flight attendants.

Flight 51, a Boeing 737-900 carrying 144 passengers and six crew members, was diverted to Minneapolis around 7 p.m., according to an Alaska Airlines spokesman and Patrick Hogan, spokesman for the local Metropolitan Airports Commission.

The source of the odor, which Hogan described as being like “burnt plastic,” has not been identified, the spokesmen said. The flight was canceled and passengers were rebooked on other flights to Seattle.

When the plane landed in Minneapolis, it was met by several first responders, Hogan said. Eight people who reported feeling ill, including the six crew members, were medically evaluated at the airport.

Four of the crew members were taken to a hospital for further evaluation, while the other four people affected declined further medical treatment.