The company operating a firefighting helicopter that crashed into a dam in eastern Victoria says the aircraft was "performing normally" moments before the accident.

Key points: The helicopter, nicknamed "Christine", was fighting fires just north of Mount Baw Baw

The helicopter, nicknamed "Christine", was fighting fires just north of Mount Baw Baw Three men on board were taken to hospital with minor injuries

Three men on board were taken to hospital with minor injuries Six Aircranes across Australia were temporarily grounded after the crash

Two pilots and one engineer were on board the Aircrane when it crashed into a dam at Jericho, in remote Gippsland, just after 7:00pm Monday.

The three men managed to swim to the edge of the dam.

Emergency Management Commissioner Andrew Crisp said the chopper "landed heavily" and the crew was flown to the Latrobe Valley Hospital for treatment.

"They were examined for some minor injuries and shock, as you'd imagine, but I believe they've been released from hospital now," he told ABC Radio Melbourne.

He said the cause of the crash was not yet clear.

Fleet grounded as 'precaution'

The Aircrane helicopter is one of the largest water-bombing aircraft in the world, and Victoria contracts two Aircranes as part of its firefighting fleet.

Five similar Aircranes — in NSW, South Australia, Western Australia and Victoria — were grounded while the crash was investigated.

The crashed helicopter is described as a "significant asset" in Victoria's firefighting fleet. ( Supplied: Uniform Photography )

Kestrel Aviation managing director Ray Cronin, whose company manages the fleet, said the ground was a "precautionary measure" while the company interviewed the crew and determined a probable cause.

He said after an initial investigation, the company and authorities had agreed that the grounding of the Aircrane fleet would be lifted.

"The Aircranes will return to service almost immediately," Mr Cronin said.

"The crews are with the aircraft ready to rejoin the fire fight in Victoria."

He said while he did not want to pre-empt the outcome of the Australian Transport Safety Bureau's (ATSB) investigation, he understood "the serviceability of the Aircrane" was good at the time of the crash.

"These environments are very challenging, very dynamic, and we are confident that the aircraft was performing normally up to the point of impact," he said.

"[I'm] absolutely confident in the aircraft — they're a workhorse, they're a very reliable aircraft."

A 'hazardous operating environment'

The Aircrane was refilling its water at the time, Forest Fire Management Victoria deputy fire officer Darrin McKenzie said.

"So they're actually quite close to water at that point. They have a snorkel which drops down into the water. They haven't fallen a great distance before they impacted with the water," Mr McKenzie said.

He said it was a "hazardous operating environment".

"This dam is surrounded by trees, and surrounded by hills. But it is quite rare that we have an event like this," he said.

"So they have to be really careful about what the wind conditions are, any downdrafts. So wind and visibility are the key things they need to think about from a safety view."

Work will begin in the next few days to try and work out how to get the Aircrane out of the water.

Crash 'very unusual' for renowned Aircrane

With a water-holding capacity of up to 9,000 litres, the Aircrane is popular with firefighting agencies around the world, CFA incident controller Mike Owen said.

"They're renowned across the world for their large firefighting capability and they operate in the USA, Canada, Australia, Greece, France and there's a fleet of about 20 of these worldwide at any time operating across firefighting," he told ABC Radio Gippsland.

"So very specialist equipment, very reliable, and Erickson are a well-known, well-respected company that operates them."

Each Aircrane is worth about $30 million, which Mr Owen said indicated the "sophistication" and "reliability" of the aircraft.

"It's very, very unusual to have an incident like this," he said.

Firefighters have been battling three fires near the Thomson Dam in eastern Victoria. ( ABC News )

Hundreds of hectares continue to burn

The helicopter was one of 10 water bombers being used to contain the Thomson Catchment Complex fires, which are burning just north of Mount Baw Baw.

Mr Owen said the fires were in a rugged area, making it difficult to get equipment into the area.

"There are three fires that are in the catchment … and together they're about 700 to 800 hectares at the moment," he said.

"[Monday] was the start of a concerted effort to use lots of aircraft bombing it, trying to create lines and assisting firefighters on the ground when we can get them in."

Premier Daniel Andrews said the crash was "a really serious incident" and said any lessons learnt during the investigation would be taken on board.

"We're very pleased obviously that nobody was seriously injured. It could've been a very different outcome," he said.

WorkSafe has been notified of the crash.