A bus rolled over a highway embankment in San Diego County, California that left three people dead and 18 others wounded on Saturday, according to the North Country Fire.

According to the north of San Diego, North County Fire Protection District spokesman John Choi, several passengers were thrown from the bus, and one of the dead was trapped under the vehicle after it landed on its roof shortly after 10 a.m. off. interstate 15 in Pala Mesa, an unincorporated community about 45 miles (72 kilometres).

There were no seat belts on this bus, Choi further added.

Another person who died was trapped inside the bus, he noted.

The injured were taken to three hospitals with varying injuries, Choi said.

It was still unclear where the bus was headed. Authorities have not released the name of the bus owner.

Choi said rescue crews were concerned that the bus may slide farther down the embankment and had to secure the vehicle before using ropes to pull up the victims to the roadside.

He said crews planned to pull the bus from the embankment and recover the body pinned under it.

The crash caused southbound traffic on I-15, a major route connecting San Diego to inland regions of Southern California, to back up for miles.

In 2017, a trucker charged with killing 13 people after a Southern California tour bus rear-ended his big-rig on a freeway in 2016 was arrested in Georgia.

The crash left the bus driver dead and a dozen passengers injured about 30 other people, including Guilford.

(With inputs from agency)