(CNN) Mitchell Lee was in an apartment across the street from the dorms at the University of Nevada, Reno, on Friday when his building shook.

At first, the university senior "thought it was like an earthquake or car crash," Lee told CNN affiliate KRNV.

Across the street, something had exploded in the basement of a seven-story residence hall, causing major damage to the building where summer school students were staying.

Authorities say there were two explosions -- a small one that prompted a 911 call to the fire department and a larger one after firefighters arrived that blew out a side wall of the building.

Investigators are still working to determine the cause of the explosions, but it is believed there was a mechanical failure in the building, said Steve Leighton, an operations chief with the Reno Fire Department. The campus police department referred to the second explosion as a "major utility incident."

Eight people were injured in the explosions, Leighton said. Two of the injured were sent to an area hospital, where they were checked out and released, he said.

"The buildings are being checked floor by floor by fire and emergency crews for structural damage and for any remaining occupants," said Jon Humbert, a spokesman for the city. "Our main focus is public safety and completing the search of the building. No one is missing."

'A quarter of the dorm was gone'

Colin Kosaka, who lives in an apartment near the university, told CNN affiliate KOLO the noise from the incident sounded like "like a car accident."

"It was a pretty big impact ... It just shook the entire apartment," Kosaka said.

Kosaka said he walked outside towards the school and saw some people running towards a residence hall while others were standing, watching smoke coming from the building.

A photo taken after the possible explosion shows smoke coming from Argenta Hall.

"A quarter of the dorm was gone," he said.

Classes have been canceled

Officials canceled classes and told employees to go home.

Harrison Wier, an intern with the university's athletic department, is staying on the second floor of the dorm. He said people had no idea what was going on when they heard the fire alarms.

"We just started walking out of the building, I even saw some staff members walked out with their hands up, we had no idea what was going on at first but five minutes after we were outside there was glass shattered everywhere," Wier said.

According to Wier, the building houses many student athletes that are there for the summer, as well as some international students.

"There was about 100 of us in the building today, but I don't know if anyone is left in the building," Weir said.

Argenta Hall can house up to 750 people.

Nye Hall was also damaged by the blast, officials said. No one there was injured.

CORRECTION: A previous version of this article misspelled Colin Kosaka's last name.