OCEANSIDE -- Two men were killed Saturday when they lost control of a rental truck on an onramp, skidded off an embankment and hit a tree, authorities said.

The single-vehicle accident happened at 4:47 p.m. as the driver of the Ryder truck took the ramp from southbound Interstate 5 to eastbound Highway 78, California Highway Patrol Sgt. Scott Payson said.

"It appears it was going a little too fast and was loaded with food," Payson said.

The names of the victims were withheld pending notification of their families.

The driver lost control on the curve and the vehicle's brakes locked, Payson said. It fell over on its side and slid across a raised dirt median and the onramp from Vista Way to southbound I-5, then pulled down a guardrail and went down an embankment, Payson said.

The truck hit a large eucalyptus tree smashing the cab nearly flat and trapping the men inside, he said. The truck came to rest north of the Buena Vista Lagoon.

Another pickup driver coming onto southbound I-5 just barely avoided a collision with the out-of-control truck.

Rob Dubar, 32, of Huntington Beach was driving behind the Ryder truck as it took the transition ramp. He said he saw the accident and called 911.

Dubar and the pickup driver ran down the embankment to the Ryder truck to try to assist the men and found them barely alive, Dubar said.

"The whole cab was crushed," Dubar said.

Oceanside police Officer John McKean said he was the first officer on scene, and he told the two men to get away from the vehicle in case it continued sliding down the incline.

Firefighters got on scene and secured the truck with a cable to make sure it wouldn't keep sliding down, Fire Capt. Ken Matsumoto said. Paramedics pronounced both men dead shortly afterward, he said.

Both men were crushed in the cab, Matsumoto said. Firefighters pulled them from the mangled wreckage, he said.

The freeway onramp was closed for several hours for the accident investigation.

Contact staff writer Yvette Urrea at (760) 901-4076 or yurrea@nctimes.com.