DENVER (AP) — Firefighters extinguished a blaze that torched several rows of seats and a suite area at the Denver Broncos’ stadium on Thursday.

The fire broke out on the fourth level at Empower Field at Mile High just after 2 p.m. and spread to the third level, where it burned at least six rows of seats in two sections. Firefighters quickly brought the blaze under control but were trying to determine if it had spread to other areas of the football stadium, which seats 76,125 people.

Stadium officials said in a statement on Twitter that the fire occurred in a construction zone near the East Club Lounge. At least 100 people were attending an event on the second level, but the stadium was otherwise empty.

About 75 firefighters were on scene at the height of the blaze. No injuries were reported.

Footage from a news helicopter showed several firefighters using water hoses to extinguish the blaze, which sent a large plume of black smoke billowing out of the stadium near downtown Denver. The Denver Fire Department tweeted several photos showing large flames spreading through the seating area.

Capt. Greg Pixley, a spokesman for the fire department, said it appears the fire originated in the suite but was partially suppressed by a sprinkler system. It then spread to the seats, which are made of plastic.

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“This type of plastic that the seats are composed of burns with not only significant ferocity, very large flames, but also produces a tremendous amount of black smoke,” he said.

Investigators have not said what caused the fire, which burned at least 1,000 square feet (93 square meters).

A welder’s torch was blamed for starting a similar fire that burned plastic seats in the west stands of the old Mile High Stadium in January 2002.

“Our firefighters have an experience with this type of fire fight. … Any time that you have a fire on an upper level, you’re going to have to move a great deal of equipment to that environment. So our firefighters brought a number of heavy pieces of hose and equipment, saws and the like, to be able to help them extinguish this fire,” Pixley said Thursday.