A serial arsonist is thought to be behind at least 10 fires set on Beacon Hill since July 14, including a blaze that destroyed a multistory construction site on Thursday morning, and the Fire Department is urging vigilance.

Stay vigilant and reduce the risk of arson on your property, the department said at a news conference Thursday and in a Facebook post. No arrests had been announced as of Sunday.

Investigators determined the Thursday fire on Sturgus Avenue South at the north end of Beacon Hill, which briefly shut down Interstate 90 in both directions because of smoke from the blaze, was intentionally set, according to the Seattle Fire Department. The torched townhomes have been hit three times, Q13 reported.

“The department has recently seen an uptick of set fires in the Rainier Ave. S. and Beacon Hill vicinity, with 10 confirmed significant fires,” the department said.

All ten of the suspicious fires occurred between 2 and 5 a.m. since the middle of July; the Farmer’s Market at 2119 Rainier Avenue South was targeted four times, the townhomes three and the U-Haul on Rainier Avenue South four times, fire officials said.

“If you own vacant buildings in this area, we are asking you to work hard to secure those structures. We are asking you to locate the dumpsters, recycle bins, and move them away from structures and buildings,” Fire Chief Harold Scoggins told Q13. “We’ve seen them as a target.”

The Arson Alarm Foundation and NW Insurance Council are offering rewards for information about the Beacon Hill fire or arsons in the area. Tipsters can call 800-552-7766 or submit a tip on the Arson Alarm Foundation’s website.