Fire damaged a panel on the marquee. Photo: Doreen CFA.

INVESTIGATIONS by police are underway after they were called to the scene of a fire at a Mernda COVID-19 testing site before 11pm last night.

The testing marquee was closed at the time of the fire with two security guards on duty, when one of the guards noticed the fire about 10.35pm.

The guard contacted Fire Rescue Victoria who were able to attend the scene and extinguish the fire, which caused minor damage to a panel on the side of the marquee.

Mernda and Doreen brigades were on scene.

One of the guards, a man in his 50s, was assessed by paramedics on scene, and cleared to work.

Police would like to speak to three men aged in their 20s, who were spoken to by security guards shortly before the fire broke out.

Anyone with information regarding the incident are urged to contact Crime Stoppers on 1800 333 000.