THREE family members aged between 16 and 44 have died after being found unconscious in a shed out the back of their home in Broken Hill, New South Wales.

Emergency services were called to the property on Creedon Street, in the northwest NSW mining town, about 4.30pm Thursday. The call-out came after a resident reported that three people - a father and his two sons - were unconscious in a rear work shed.

On arrival, police and paramedics located a 44-year-old man, and two boys, aged 16 and 23, unresponsive.

A Fire and Rescue NSW spokesman said "there was some sort of generator … they were overcome by the fumes".

The crews used breathing apparatuses to enter the shed and retrieved the three men, despite "difficult access", just before 5pm.

It is believed they were overcome by gas while working with an engine or generator that malfunctioned in the closed shed.

A NSW Ambulance spokesman who described the tragedy as "a hazardous material incident" said all three men went into cardiac arrest.

"All three were taken to Broken Hill Hospital but sadly passed away," police said in a statement.

Emergency services attending the scene in Creedon Street, Broken Hill tonight where a man and his two sons have been found unconscious in a shed, 28 June 2018. Picture: Myles Burt.
Emergency services attending the scene in Creedon Street, Broken Hill tonight where a man and his two sons have been found unconscious in a shed, 28 June 2018. Picture: Myles Burt.

A NSW Police spokeswoman told news.com.au the deaths were not suspicious, no one was being sought in relation to the matter, and "it was not suicide".

Officers from Barrier Police District have established a crime scene at the premises but have not yet been able to "gain access safely to conduct a full investigation".

Police inquiries are continuing and a report will be prepared for the coroner.

A father and his two sons have died after a suspected gas leak in their work shed. Picture: Myles Burt
A father and his two sons have died after a suspected gas leak in their work shed. Picture: Myles Burt