PALM SPRINGS, Calif. — At least 13 people were killed Sunday when a tour bus and a truck collided on Interstate 10 near this resort city 100 miles east of Los Angeles, authorities said.

California Highway Patrol Border Division Chief Jim Abele says the early Sunday crash just north of Palm Springs injured an additional 31 people.

He says the USA Holiday tour bus was returning to Los Angeles after a visit to the Red Earth Casino in Thermal, California.

He added the bus was traveling much faster than the semi, and the impact was so strong the bus went about 15 feet into the trailer. He says it's not clear if the bus was speeding.

Abele says it's unknown if alcohol, drugs or fatigue played a role in the accident. The bus was inspected in 2014, 2015 and this year and found no mechanical issues.

The California Highway Patrol officer Stephanie Hamilton said all the fatalities were traveling in the tour bus.

Hamilton said the death toll could rise as rescuers make their way through the tangled crash scene.

"The intrusion into the bus compartment is significant," Hamilton said. At least 25 bus passengers were taken to Palm Springs area hospitals, she said.

Throughout the morning, firefighters struggled to reach victims. The bus crashed into the big rig's trailer, and a tow truck was used to lift the trailer and help officials gain easier access to the demolished vehicle. Another tow truck tried to pull the big rig forward, off the bus. Firefighters positioned ladders in the bus' windows to pull victims out.

All westbound lanes of I-10 were closed at Indian Canyon following the crash.

The tour bus belonged to USA Holiday, a Los Angeles-based tour company, and Hamilton said the driver was identified as one of its owners. The bus was carrying about 30 people and may have been coming from Red Earth Casino, near the Salton Sea, CHP said.

USA Holiday regularly carries passengers from the Los Angeles area to Southern California casinos. According to its Facebook page, USA Holiday has recently made trips to Tortoise Rock Casino, Red Earth Casino and Las Vegas.

Chris and Rachel Williams were delivering frozen chicken to Los Angeles when they got stuck in traffic. They were about five vehicles east of the scene and waited more than an hour as traffic backed up.

"We're doing good. We're just saying our prayers for the people involved in this situation," Chris Williams said. "This is a day that will be remembered."

The crash was among the deadliest in California in years. In April 2014, 10 people were killed in a fiery crash near Orland, Calif., when a FedEx tractor-trailer crossed a narrow median on Interstate 5 and slammed into a bus carrying high school students from Los Angeles who were on their way to visit a college campus. The National Transportation Safety Board investigated that collision and said more than a year later that it was a mystery why the truck driver had crossed the median.

Following that crash, the NTSB also urged the National Highway Traffic Safety Administration to require secondary doors as emergency exits on new bus designs.