A bomb scare which shut down Victoria's Avalon Airport for several hours on Thursday was caused by a passenger's laser hair removal device, police have revealed.

Hundreds of travellers were evacuated and prevented from entering the airport, south-west of Melbourne, on Thursday morning, as emergency crews rushed to the scene.

Dozens of responders, including members of Victoria Police's Bomb Response Unit, were called to the airport shortly before 6am. 

The suspicious item in a passenger's bag had activated alarms during the security screening process, and a man was detained at the scene.

'The building has been evacuated and the area cordoned off as a precaution while the investigation is ongoing,' a police statement said.

Police later confirmed: 'The Bomb Response Unit conducted checks on an item and it was determined to be a laser hair removal device.'

The personal beauty product retails for up to $1,000 and promises results similar to salon laser treatments and used as an alternative to shaving. 

The domestic terminal has since reopened after police declared the item posed no threat.

Prospective travellers were prevented from entering the airport for four hours, while incoming passengers were also affected.

A flight from Bali landed about 7am, with passengers safely disembarking before being escorted out of the terminal and taken to a temporary holding area in the car park.

Passengers with access to vehicles were allowed to leave immediately, while others were directed to the main exit.

Those arriving from Bali were told there was a security incident affecting the domestic terminal, which had been shut down.

International flights continued to be processed as normal.

Passengers scheduled to fly to Brisbane were denied entry.

Long queues of cars formed along Canberra Drive and Beach Road as the disruption continued.

'Everyone is being turned away and asked to park on the road,' one man told local radio station Bay 93.9.

'We pulled up next to someone who said it was apparently a bomb scare.

'There's cars everywhere outside.'

Another traveller told 3AW: 'There's people queued up for miles. They blocked it off at the entranceway where the roundabout is. We've been here for at least an hour now.'

A flight to Avalon that was scheduled to leave Sydney at 8.10am was delayed by two-and-a-half hours.

Social media also carried claims of flights being cancelled. 

'We arrived at the airport at 5.50am,' one man wrote online.

'At 6.05am we were evacuated to the drop off point. Once police arrived, they arrested a guy for questioning and we were moved further back to the short term car park. 

'Once we were told our flight was cancelled and we were put on another flight, we left.'

An Avalon Airport spokeswoman confirmed the security scare.

'The domestic terminal at Melbourne Avalon Airport was evacuated this morning following the identification of a suspicious item during the screening process,' she said.

Today's response demonstrates the vigilance of the screening and security processes, with precautionary measures taken immediately to ensure the safety of passengers, staff and the broader community, which will always remain our highest priority.'

Jetstar sent text messages to passengers.

'There is a security incident at Avalon Airport this morning and the airport is currently closed. There are also road closures around the airport to be aware of,' it read.

'Chat with us here (link) for flight options from Melbourne. We apologise for the inconvenience and thank you for your patience.'