MINNEAPOLIS (WCCO) — An Alaska Airlines flight from Chicago to Seattle was diverted to the Twin Cities Wednesday evening after passengers and crewmembers were having difficulty breathing due to a mysterious odor.

Alaska Airline officials say the Boeing 737-900 departed from Chicago at 5:48 p.m., and landed at MSP Airport at about 7:17 p.m.

Four of the six crewmembers were taken to the hospital after landing. Two other crew members and two passengers were evaluated at the airport and deemed to be OK.

All 144 passengers had to find a different flight to get to Seattle. The cause of the odor is still under investigation.