VISTA (CNS) - Fire officials believe a two-alarm blaze at a vacant business in Vista was intentionally set, a sheriff's sergeant said Wednesday.

CBS News 8 acquired cell phone video of the fire captured by a witness who was at the scene. It shows a vacant building going up in flames at the Vista strip mall.

The former pot dispensary went up in smoke and firefighters had to go into 'defensive mode'. 

A witness told authorities a man wearing an oversized black t-shirt and jeans was standing in front of the building at 631 S. Santa Fe Ave. shortly before it went up in flames around 10:20 p.m. Tuesday, according to sheriff's Sgt. Dwain Washington.

Washington said firefighters who extinguished the blaze were treating its cause as arson. The sheriff's department's Bomb/Arson Unit was summoned to further investigate.

Vista, Oceanside and other fire departments joined forces. It took nearly three dozen firefighters to stop flames from spreading to an immigration office and construction company next door. 

Anyone with information on the fire was asked to call the sheriff's department at (858) 565-5200 or Crime Stoppers at (888) 580-8477.