The driver of a cement truck was seriously injured Tuesday evening in the Bethesda area of Montgomery County when his truck overturned on a ramp from Rockville Pike to the Capital Beltway, authorities said.

The driver was extricated after being trapped for about 15 minutes in the truck, which overturned on the ramp from the northbound lanes of Rockville Pike to the inner loop of the Capital Beltway, said Pete Piringer, spokesman for the county fire and rescue service.

Piringer said the driver had suffered Priority 1 injuries — the most serious category, often indicating that a victim’s condition is life-threatening.

It was not immediately clear what caused the truck to overturn. A preliminary report indicated that the incident may have stemmed from a collision.

No other injuries were reported, but firefighters were working to contain a possible spill of fuel from the truck, Piringer said.