Suffolk fire marshals are investigating six suspicious fires that have occurred on two streets since the beginning of November.

One vacant house in the 600 block of First Avenue has been set ablaze three times since Nov. 6, city spokeswoman Debbie George said.

The house, owned by Suffolk Property Development, had fires on Nov. 6, Nov. 17 and Nov. 19.

In one of the most recent fires, at about 8 p.m. on Saturday, firefighters found smoke coming from debris that was located under the house, according to a police report.

Only about eight hours later, another fire happened at another house on First Avenue.

In a different neighborhood, in the 300 block of North Fifth Street, firefighters responded just after midnight on Monday morning for a report of smoke coming from a residence. They found heavy fire showing from the house upon their arrival. They were able to extinguish the fire quickly, but the house, which contained four apartments, was severely damaged.

Firefighters had previously responded to a fire at that house on Nov. 14.

“Fortunately, no civilians or firefighters have been injured in any of these fires, but all it’s going to take is one,” George said. Two of the homes were vacant, and the occupants were not injured at the other house.

George said fire marshals are working with “very vague descriptions” of teenage, black males seen running in the area of a couple of the fires.

Anyone who has information is asked to call Crime Line at 1-888-LOCK-U-UP. Callers to Crime Line never have to give their names or appear in court, and may be eligible for a reward of up to $1,000.

For a view of this fire from amateur videographer Mark Anderson, visit http://youtu.be/DQN9Q6XxecA.