Whoever torched two playgrounds in Laurel last month might have set five additional fires in the area since January, sometimes striking during the day and at occupied businesses, authorities said Thursday.

Fire investigators stopped short of saying a serial arsonist might be on the loose in this normally quiet city. But when that many fires break out in a small geographic area in a three-month span — and investigators have determined that at least six were set — officials said they must consider whether the fires were the work of one person or a group.

“That’s not normal,” said Prince George’s County Fire/EMS Department Deputy Chief Scott Hoglander, who heads investigations. “It’s common to have fires, but to have so many that have been intentionally set is an area of concern for us. . . . I can tell you through experience, there’s no such thing as coincidence.”

Investigators had long been probing connections between a March 3 fire that destroyed a playground at Laurel’s Discovery Community Park and a March 11 fire that ruined similar play equipment at Emancipation Community Park, but with Thursday’s announcement, officials signaled for the first time that the case might have more far-reaching implications.

Laurel Mayor Craig Moe announced that he was increasing the reward for information from $5,000 to $10,000 as he asked those who might know something to call the fire department’s arson hotline at 301-772-7766.

“It’s important for the community when they see something, they need to say something,” Moe said.

Police and fire officials declined to say how each blaze was set or what other evidence connected the fires — aside from timing and proximity.

The fires at Discovery Community and Emancipation Community parks — which Moe said caused about $275,000 in damage — were among six blazes intentionally set in the area since January and possibly connected to each other. Investigators also are probing whether a fire at Laurel Fuel Oil and Heating might be connected to the others.

They said a March 8 playground fire at Granville Gude Park is not thought to be linked. Two teenagers were charged in that case.

At a library near Emancipation Park on Thursday, Laurel residents said they wondered about the motive for setting such fires.

“It’s scary,” said Rosa Appiah, 58. “You never know who’s going to be in the building [or] in the area.”

Four of the seven blazes occurred during business hours — the two at the playgrounds, one before 4 p.m. March 22 at the stage at Granville Gude Park and one before noon March 23 at the Empire Buffet restaurant. In that case, Hoglander said, someone ignited the structure from the outside while people were inside.

Two of the cases occurred in the early evening — one about 7 p.m. March 6 at Laurel Fuel Oil and Heating and the other before 8 p.m. Jan. 10 at the Bottom Dollar grocery store on Laurel Bowie Road. In that case, Hoglander said, someone ignited trash outside the store and the fire spread to the occupied building.

Another fire was discovered before 9:30 p.m. March 20 behind an office building in the 14300 block of Laurel Bowie Road, authorities said.

No one was seriously injured in the blazes, but a firefighter hurt a shoulder battling the heating company fire. The fires caused about $600,000 in damage, authorities said.

Prince George’s County Fire Chief Marc Bashoor said that although it is too early to connect the blazes to one person or a group, the pattern is troubling. Of particular concern, he said, is the apparent “escalation” from small, outdoor fires to blazes at occupied buildings.

Each incident, Bashoor said, puts residents and firefighters in danger.

“We could be attending funerals right now,” he said.