The Bureau said the pilot of the Dash 8 advised air traffic control of smoke in the cockpit while the aircraft was about 70kms away from the capital, forcing the Wagga bound flight to divert to Canberra Airport.

The investigation into the incident, which caused no damage to the craft, is expected to take three months.

Passengers have described the nervous minutes before the plane landed.

Sydney-based real estate agent Peter O'Malley, who was seated at the front of the cabin, told Fairfax Media the aircraft's crew were "visibly shaken" as the midair emergency unfolded.

"(The lead steward) was rattled beyond normal," he said.

"This was not a standard mishap - we were told to brace for an emergency landing."

Mr O'Malley told of chaotic scenes as the plane touched down in Canberra, with passengers ordered to just "get out" with no chance to grab their belongings.

Flight QF2225 departed Sydney about 11.30am and had been due in Wagga Wagga about 12.30pm, but was diverted and landed at Canberra at about 12.45pm.

ACT Ambulance Service Intensive Care paramedics took the pilot and co-pilot to the Canberra Hospital for a checkup, with a Qantas spokeswoman confirming at about 4.30pm both had been discharged from hospital without injury.

Andrew Bradley was in the emergency exit aisle of the Qantas plane diverted to Canberra on Monday, and said it was a nervous few minutes between the pilot’s announcement of smoke in the cockpit and landing.

“He said we would land in 10 minutes - [it was] the longest 10 minutes of your life,” Mr Bradley said.

The Wagga Wagga resident said he could smell something before the announcement was made.

“You could smell something but you didn’t know what it was – when you heard it was smoke you put two and two together,” Mr Bradley said.

“We knew something was wrong when the air hostesses sat down, and they told us to ‘pack your table and sit in your seat’.

Mr Bradley, 44, said he and some business clients – returning to Wagga Wagga from Sydney after the Penrith-Cronulla NRL game on Sunday – thought their time may have come.

“We thought it could have been it – thoughts of loved ones went through your head.

“There was a bit of panic there [from the passengers], an air of what’s going on, what’s going to happen?

“The young air hostess, when she was going through the procedure she was getting upset – she got pretty shaky in the voice - so we thought it was not good, not good at all.”

The 50 passengers, including one child, landed safely.

Mr Bradley said they were greeted by a fire engine and airport support vehicle as they exited the plane by the steps as usual, before taking a 2.30pm flight to Wagga Wagga with a separate crew.

He praised the professionalism of the crew on the diverted flight.

“[They were] 100 per cent professional – we knew it was bad – but they were very, very professional and did a great job,” Mr Bradley said.

“I think a lot of people wanted to thank the pilot but nobody got the chance.”

Despite the drama in the cabin as the emergency unfolded, passenger Doug Williment, from Sydney, said the aircraft's crew handled the situation superbly.

"(The pilot) wasn't particularly alarmed but you could sense the urgency in his flying," he said.

"He landed it beautifully."

Mr Bradley said there was relief when the rearranged flight from Canberra landed in Wagga shortly after 3pm.

"When we landed it was pretty emotional, you don’t wish anyone to go through this kind of thing," he said.