NOVATO (KRON) — Five were injured, including one critically, in a Highway 37 head-on collision in Novato early Thursday morning, according to police.

The collision happened around 10:30 p.m. just west of Atherton Avenue in Novato, according to the CHP.

The collision when a  2013 Nissan work van traveling west bound on Highway 37 drifted left and into the wide grassy center divide area for an unknown reason, officials said.

The van traveled through an opening in the guardrail and hit a portion of it before colliding head on with an eastbound 2014 Cadillac Escalade.

The driver of the van was critically injured and taken to Marin General Hospital where we was treated for injuries considered life-threatening.

The Cadillac’s driver, a 46-year-old Phoenix, Arizona resident, and his 46-year-old wife and two sons, ages 7 and 11, were taken to Novato Community Hospital with injuries ranging from minor to moderate.

The cause of the collision remains under investigation.