Two police officers were injured and a man is suspected to have been killed in the explosion which happened after a seven-hour siege at a property west of town.

 Derrinallum CFA member Geoff Henderson said the sound of the explosion "threw him out of bed" just before 1.30am.

"It was very very loud, people have been saying they heard it across country 20 kilometres away," Mr Henderson told The Standard. 

He said by the time he had thrown on a pair of shorts and a shirt his phone was ringing. 

"My son lives behind the house. He said to me "the house is on fire and the shed is gone.

"I told to him call triple zero and let them make a decision." 

"Shortly after we were activated as a brigade and called out." 

Mr Henderson said they received special instructions that CFA volunteers were not to arrive in private vehicles and were to follow police instructions. 

He described what he saw as "utter devastation". 

"They took us to a certain point and just told us to wait. We were there for about three hours and just waited. They couldn't let us into the scene for safety reasons.

"Then they said there's nothing we can do until daylight and we were stood down. It was burning when we arrived, but it was out pretty quickly. For its size it was the quickest fire I've seen." 

Mr Henderson said he was feeling "pretty flat" on Saturday afternoon. 

"I'm devastated. I knew him (the owner of the property) and it's sad that it came to this. It's just one of those things that you don't need happening.

"It's been pretty quiet today. The highway is closed and I think everyone is in a little bit of shock."

Derrinallum Post Office owners Margaret and Larry Howard said they often heard smaller explosions from the property. 

Mrs Howard was woken by the noise but Mr Howard said he slept through it. 

"He used to do a lot of his work at night and every now and again you'd hear a couple of explosions from up there," Mr Howard said. 

"My wife heard the explosion but I didn't know anything about it until someone mentioned it while I was out walking this morning. 

"I jumped on the internet when I got home and was quite shocked when I found out what happened. It's a sad situation." 

Mr Howard said he noticed police near the house last night, but didn't think anything of it until now. 

"We went over to Camperdown and noticed the lights up there," he said. "When we came home just after 11pm, they were still there which I thought was unusual but didn't think anything more of it." 

jwoolley@fairfaxmedia.com.au