Mr. Beef and Gyro sustained damage following a gas explosion on Monday, May 1. (Photo by Erika Wurst / for Chronicle Media)

Nicor is investigating a possible natural gas explosion that blew the windows out of two Oswego businesses in the early morning hours of Monday, May 1.

Oswego Fire Protection District firefighters were alerted of the structure fire at a strip mall in the 300 block of Douglas Road around 3:50 a.m.

Three engines, a ladder truck and two ambulances responded to the scene and found that the front windows of two businesses had been blown out, and a small fire had started inside.

No one was inside the affected businesses, which were identified as Mr. Beef and Gyro, and a vacant attached business directly to the south. A third establishment, Windy City Pizza, sustained minor damage in the blast.

According to fire officials, the gas to the building was shut off and the fire was brought under control.

Both Mr. Beef and Gyro and the vacant business space sustained significant structural damage, fire officials said. A damage estimate was not available.

The Oswego Fire Protection District, along with Nicor, continue to investigate the cause of the explosion.

The Montgomery-Countryside Fire Protection District and the Bristol-Kendall Fire Protection District provided coverage for Oswego fire stations while Oswego firefighters responded to the explosion call.

— Oswego businesses damaged by gas explosion —