A natural gas explosion leveled a house and injured 15 people, two critically, after a gas main break Tuesday near the New Jersey shore.

Seven of the injured were gas company workers trying to locate the source of a leak that filled the neighborhood with a strong gas smell. Two of them were in critical condition at a hospital in Atlantic City.

Six firefighters and two emergency medical service technicians also were injured, sustaining concussion-like symptoms from the shock wave. Among them was Stafford Township Fire Chief Jack Johnson, who was about 50 feet from the home when it blew up.

The cause of the 10:32 a.m. explosion had not been determined.

Houses on either side of the one that exploded were badly damaged, as was a partially built one across the street. Stafford Police Capt. Tom Dellane said other homes located within several blocks of the the blast, which he termed “a very large explosion,” suffered varying degrees of damage.

The two most seriously injured gas company workers were taken to a trauma center in Atlantic City, where one was listed in critical condition and the other in critical but stable condition. Johnson said those workers were about 20 feet from the house when the explosion occurred.

The firefighters and EMS workers sustained concussion symptoms and complained of problems hearing after the blast. All but one had been treated at local hospitals and released by mid afternoon.

Dellane said the home had been undergoing renovations but was unoccupied at the time. The blast occurred about an hour and a half after police received the first report of a strong gas smell in the area.

Emergency crews and gas company personnel responded and began evacuating 75 to 100 nearby homes. About 300 homes remained without gas service

(Inputs from AP)