Canberrans returned from trips interstate, gearing up to unpack and get ready for work on Monday.

Others left, farewelling friends and family and looking forward to milder weather in Brisbane or Melbourne.

Around lunchtime, people lined up at the Qantas check-in kiosk, checking their phones for a last-minute cancellation or delay.

An ordinary-looking man in a white shirt walked up to the wide glass windows at the domestic terminal.

And he shot a gun.

READ MORE: Canberra Airport evacuated after 'calm' gunman fired five shots

Inside the departures lounge, Peter Foong wondered why there was construction work happening on a Sunday.

He saw people running, and initially assumed they were late for a flight.

"And then I thought, no, they were running really quick," he said.

"People were saying 'drop down, drop down, get behind something'."

Even when Peter took refuge behind his small wheelie suitcase, and heard panicked cries ring out through the vast airport, he didn't think it could really be gunfire.

"This can't be right. This is Canberra, things like this don't happen," he said.

In a bathroom, Melbournian Daniel Knol was blissfully unaware of the chaos outside. He washed his hands and wandered out.

"I noticed that people were hiding under the long seated area, which I thought was a bit odd," he said.

"Then I started to hear a couple more bangs."

People started to run, and so Daniel followed. But he couldn't see his husband Carl. Panicked, he called out Carl's name.

Along with around "fifty or sixty" other people, the couple cowered behind a customer service desk.

"Children crying, and parents crying," Daniel recalled.

Calm and courageous, airport crew ushered scared crowds into rooms and behind desks.

Downstairs, Holder man Vishal Jadha was waiting for his partner in the arrivals lounge.

He heard gunshots. And then weeping. Elderly people were being evacuated, but many struggled to rush down the stairs.

Vishal ran up to help them. He noticed a woman with young daughters, screaming.

The family were only metres away from the shots being fired, Vishal said.

He saw the windows that had been fired at. They were not shattered, but there were clear bullet marks in the glass.

And then he saw the alleged gunman. Vishal described the man as middle-aged, in a white shirt and goggles.

Unnervingly, he was "really calm".

"He was just wearing his jacket, standing there like a normal person," Vishal said.

Passengers departing the stairs of a parked plane that had just were turned around, doors locked behind them.

The gunfire stopped, and crowds were evacuated.

Police apprehended the man, holding him to the ground. He did not resist arrest, they said.

As he ran outside, Peter took photos of items that had been abandoned. Bags, jackets, suitcases, phones.

At the security checkout was a lone shoe.

Some people went home. Others waited, hoping their cancelled flights would be replaced. Most were shaken.

Selena Lee, who had ran for an exit before taking refuge in a parking lot, said she thought she was going to die.

Hours later, when the airport terminal reopened, people were let through to catch the first flights or to pick up unattended items.

Four prams, covered in blankets and women's coats, were lined up to be collected.

Behind them are wide and clear airport windows. A Qantas plane is ready to be boarded.

And for a few minutes, before being hidden behind a grey cloud, is a bright and colourful rainbow.

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