Two Illinois high school students were killed in a sledding accident on spring break in Colorado, school officials said.

The male students were identified only by their ages, 17 and 18. They were students at Prairie Central High School in Fairbury, Illinois, school administrators said.

They were riding in tandem down the halfpipe at Copper Mountain Ski Resort in Summit County when they launched off a large snowbank at the bottom, the Summit County Sheriff’s Office said.

The accident at Copper Mountain, a resort less than 80 miles west of Denver, happened about 8:30 p.m. Sunday, officials at the ski area said.

Copper Mountain said in a statement that it has a “sledding zone” but that the activity is otherwise prohibited in multiple areas.

The halfpipe closes at 4 p.m. each day, and the feature is off-limits to sledders at all hours, in any case, the resort said.

“Safety is top priority at Copper Mountain, and we ask our guests to please observe posted signs and warnings and not enter closed trails and areas,” it said. “Copper Mountain closes all lift and trail access at 4 p.m. daily, including the halfpipe, which was closed and roped off at the time of the incident.  

They struck hard ice, the sheriff’s office said, according to NBC affiliate KUSA of Denver, and were declared dead at the scene.

The Summit County Coroner’s Office was expected to determine the cause of death.

Dustin Lyman, the resort’s president and general manager, said in a statement that “the entire team at Copper Mountain is deeply saddened by this tragic incident.”