LITTLETON, Colo. -- Firefighters battling a reptile shop fire were forced to retreat by snakes on the floor and thick smoke, a chief said Tuesday.

The early-morning fire, which killed about 3,000 snakes, appears to be accidental, Littleton Fire Division Chief Jim Hofstra told 7NEWS.

The fire triggered an alarm at 5:39 a.m. Monday in a warehouse at 3911 Norwood Drive. The fire badly damaged the Pro Exotics reptile store and caused less damage to other businesses in the warehouse.

"The heavy smoke, confusing layout and presence of snakes on the floor led responders to pull out and begin defensive fire suppression tactics," Hofstra said in a news release.

Hofstra told 7NEWS that investigators believe the fire began in a U-shaped warehouse area where snakes were kept, behind the store's office.

"They're going to pinpoint exactly what was there -- what equipment, what furnishings," which included warming lights for the snakes, Hofstra said.

"I would think we'll have a pretty good idea (of the fire's cause) in the next day or two," he said, adding that "there's nothing suspicious" about the fire.

Pro Exotics' owners said about 3,000 non-venomous snakes were kept in containers stored in racks throughout the warehouse unit, Hofstra said.

Almost all of the snakes died, but a small number of snakes were found alive, including a large boa constrictor that two firefighters carried from the warehouse ruins.

Also rescued from the unit were several incubation containers holding snake eggs that may survive, Hofstra said.

The shop specializes in breeding high-end exotic snakes, some worth more than $20,000, according to Chad Brown, a Pro Exotics co-owner, former NFL linebacker and University of Colorado graduate.

"This is a huge loss for our business," Brown said. "We had a number of unique animals."