Friends and other avid aviation enthusiasts have thrown their support behind the pilot who was among five people killed in a plane crash into a Melbourne shopping centre yesterday.

Australian Transport Safety Bureau (ATSB) Chief Commissioner Greg Hood today said the Essendon crash would be fully investigated, and refused to comment on reports that pilot Max Quartermain was under investigation for a 2015 incident.

“We’ll look at maintenance records, the history of pilot, the history of aircraft… at this very early stage, we’re not going to speculate in relation to any specific part of the investigation,” he said.

Max Quartermain was killed when the plane he was piloting crashed this morning. (Facebook)

“We’re a no-blame investigator. It’s in our legislation. The investigators are trained not to put any bias in what is the obvious. When you’re investigating a transport accident, you remain completely objective.”

Comm. Hood said a preliminary report would be released in 28 days, but the final report would take much more time to complete due to the “complex nature” of the investigation.

Chris Cowan, Essendon Fields CEO, said Mr Quartermain was “well respected by the Essendon aviation community”.

Mr Cowan said counselling has been offered to witnesses and other affected people, and said DFO would be closed as a mark of respect until further notice.

He also said renewed safety concerns over Essendon Airport were not warranted.

“The airport has a enviable safety record. The reality is airports and cities mix, that’s a reality of modern day life,” Mr Cowan said.

Earlier today, Premier Daniel Andrews said the airport was an integral part of the state’s transport infrastructure and acted as a base for emergency services.

“It’s a very important part of our transport infrastructure, it’s a big employer, it’s no small thing to be talking about the future of the Essendon Airport,” he told the TODAY Show.

“The most important thing is to get the facts. Let’s establish exactly what happened here… let’s let [authorities] do their important work and wait and see what the facts are.”

READ MORE: Airport safety concerns

Overnight, reports emerged that Mr Quartermain was involved in a “near-collision” in 2015, when he reportedly flew with a faulty GPS and narrowly missed another aircraft during a Mount Hotham flight.

A large hole in the DFO building. (9NEWS)

Mr Quartermain’s close friend Phil Wall said he had flown all over Australia with the father-of-two and veteran pilot, and has no doubts over his safety precautions.

“He never took any risks. He was a risk-free pilot,” Mr Wall told the TODAY Show.

“He’s very thorough. He wouldn’t put people in the risk of danger. Many, many times we’ve unpacked the plane because Max wasn’t happy. We wouldn’t leave the tarmac until everything was spot on.

Mr Quartermain had been a charter pilot for more than 38 years and has an "impeccable safety record", according to his company's website.

Other friends have remembered him as a "true aviator" with a "gentle, caring nature".

The crash caused a large explosion. (9NEWS)

Aviation expert Geoffrey Thomas told 9news.com.au the plane recently passed a safety check and that Mr Quartermain was a re-endorsed as pilot.

Mr Quartermain's four passengers – Glenn Garland, Greg De Haven, Russell Munsch and John Washburn – were US citizens who were headed to Tasmania's King Island on a golf trip.

Their light plane had just taken off from Essendon Airport when Mr Quartermain made two mayday calls. It then crashed into the rear of DFO Essendon, near the Spotlight and Focus on Furniture shops.

Mr Andrews has described the crash as the “worst civil aviation disaster in 30 years”.

Witnesses described seeing the explosion upon impact, with thick black smoke and a “fireball” leading some to describe the scene as “like a movie”.