Avalon and Melbourne International at Tullamarine continue their daily operations despite anonymous threats sent through The Herald against them.

The threat, which was in a letter form, prompted the police to crowd both airports.

The letter appeared precise and talked about the weapons to be used for a planned attack. The Herald, on the other hand, refused to disclose its full content to the police.

"Police are evaluating the threat and working closing with the AFP and airport security to ensure community safety," a Victoria Police spokeswoman said.

Justin Giddings, Avalon's CEO, told 3AW that there had been no delays or cancellations at the airport. He confirmed no disruptions to flights this morning.

"We have increased security. There have been no cancellations, no delays, terminal evacuations or road closures,” he explained.

Qantas informed its passengers through Twitter, it is "business as usual" for Qantas flights at Melbourne Airport and Jetstar services at Avalon.

A Channel 9 helicopter pilot flying over the scene at Avalon reported that the incident did not affecting airport operations, notwithstanding at least six police cars at the scene.

Ross Barker, Channel 9’s pilot, told his network “It doesn’t appear the roads are blocked, but there is a heavy police presence.”