One large fireworks mortar landed on a flat roof of a three-story apartment complex, penetrated 9 inches of roofing and exploded inside an apartment, igniting a fire, Denver officials say.

It was one of 25 fires ignited Monday in Denver. Many more were reported across the wider Denver area on Independence Day.

In 2014, there were 14 fires reported in Denver; and 16 in 2015, said Melissa Taylor, spokeswoman for the Denver Fire Department.

The growth in the number of fires on the Fourth of July is a troubling sign that Denver city fines of up to $999 and terms of up to one year in jail are not dissuading revelers from using illegal fireworks, some which are very powerful and dangerous in the wrong hands, Taylor said.

“People are not taking our advice and leaving fireworks to the professionals,” she said. “It’s an odds game. People don’t think they will get arrested, and they don’t think they’ll start a fire.”

A spike in the daily count of fires is not unusual for Independence Day, or for other holidays like Thanksgiving when cooking increases, Taylor said. In 2015, Denver firefighters responded to an average of five fires a day, or 1,792 the entire year, she said.

But the total Monday was five times the normal level, nearly twice as many as in 2014, she said. Not all fires are linked to fireworks, and some are only suspected. In some cases, people put smoldering fireworks into Dumpsters igniting trash fires. In many instances, fireworks spewing sparks through the air start dry grass or bushes on fire.

The apartment fire was reported at 12:40 a.m. at 1245 N. Lafayette St., Taylor said.

“That one could have been very serious,” she said. “Luckily no one was in the room where the mortar exploded. If they had, they likely would have been seriously injured.”

Denver firefighters were on the scene in minutes and were able to extinguish a fire it caused while it was still small, she said.

A large fire was also reported in a grass field on the border of Denver and Aurora at South Havana Avenue and East Yale Avenue, Taylor said. Both Aurora and Denver firefighters responded to the blaze that blackened a large area of ground.

“I’m surprised by this year’s numbers, because it’s a little bit greener this year than it has been the last few years,” Taylor said.

Another large grass fire in Lakewood burned 3 acres late Monday after people celebrated the Fourth of July.

Although the cause of the fire near Kipling and Quincy is unknown, it was one of numerous grass fires that happened as people celebrated with fireworks Monday night.

West Metro Fire Rescue dispatched six engines and three brush trucks to the fire. The fire was 100 percent extinguished early Tuesday morning, according to a 12:11 a.m. tweet.

Crews on the ground, getting a knock on 3 acre grass fire near Kipling & Quincy. pic.twitter.com/wWxzyQB7xF — WestMetroFire (@WestMetroFire) July 5, 2016

A fire investigator was trying to determine the cause of the 3-acre fire in Lakewood, according to a West Metro tweet.

Fireworks + Bushes = A fire that almost damaged a home. Please be careful. pic.twitter.com/5pZSZKILtO — SouthMetroFireRescue (@SouthMetroPIO) July 5, 2016

Updated July 7, 2016 at 12:23 p.m. The following corrected information has been added to this article: Because of a reporting error, Melissa Taylor’s title has been corrected to spokeswoman for the Denver Fire Department.