Two buses are involved in the crash. Seven injured people are being taken to Bridgeport hospitals. There are 56 other passengers who have declined medical care, officials say.
A witness said a white bus without a visible company name apparently rear-ended a bus belonging to the Dartmouth Bus Co.
Four of the injured have been brought to Bridgeport Hospital.
EMS units from several towns are on the scene, along with firefighters.
A haz-mat team from the state Department of Energy and Environmental Protection is enroute, officials said.
Traffic is at a standstill in the area of Exit 32 on the southbound side of the highway. The left and center lanes are closed and vehicles are squeezing by in the right lane and shoulder.
Traffic is now backed up for more than five miles, to the Milford Parkway connector at Exit 38iobacked up to Exit 35, Schoolhouse Road, in Milford.
Avoid the area if you possibly can.