Part of the four-lane Interstate-5 highway bridge over a river in Washington state collapsed Thursday, sending vehicles and drivers plunging into the Skagit River, officials said.

As of 11 p.m. PDT, there were no fatalities, but two of three people rescued from the cold water were hospitalized for hypothermia, The Washington Post reported.

Several witnesses told local TV stations that a truck carrying an oversize load struck the bridge while crossing it just prior to the collapse, the Chicago Tribune reported Friday. Other witnesses saw girders falling.

The bridge runs between the towns of Mount Vernon and Burlington, about 55 miles north of Seattle.

Investigators indicated it was far too soon to definitively determine the cause of the collapse, Jim Martin, a Skagit County spokesman, said.