Tigerair customers face flight delays this morning after a security threat at Melbourne Airport last night.

Security was alerted to the threat late last night, prompting the cancellation of several departing flights.

TT206 from Melbourne to Sydney and TT221 Sydney to Melbourne were cancelled early this morning and nine other Tigerair flights are facing delays of between 25 and 230 minute due to the security issue.

Customers are urged to contact Tigerair if they have any questions about flights.

Authorities have now confirmed the airport was not evacuated during the scare.

Do you know more? Send an email to contact@9news.com.au

Tigerair Australia CEO Rob Sharp said all necessary steps were taken by the airline to implement precautionary measures and ensure passenger safety.

He thanked Australian Federal Police and Victorian police who were sent in to search the terminal following the threat.

"Tigerair also apologises to affected passengers for the inconvenience and is doing everything possible to get them to their destinations as quickly as possible," Mr Sharp said.

Victoria Police, Australian Federal Police and airport security attended Terminal Four at Melbourne Airport over an undisclosed issue. (9NEWS) (9NEWS)

Victoria Police are investigating.

Earlier a Melbourne Airport spokeswoman Anna Gillett told Fairfax Media Tigerair flights were cancelled as authorities responded but would not provide an exact reason for the six-hour shut down.

Ms Gillett said the airport never releases details on security issues.

While officials would not confirm the nature of the incident passengers tweeted from the Tullamarine tarmac saying they had been warned about a possible bomb threat.

Passenger Scott Marquardt tweeted he was on "Tigerair flight 539".

"Announcement of POSSIBLE bomb threat at Melbourne airport made by flight crew," he wrote. "So my plane is sitting on the Tarmac."

Passenger Corey Ginnivan tweeted he was also stuck on the runway due to a federal police action but was waiting to be evacuated on bus.

"Currently stuck in the plane on the Tarmac because there's been an "incident" and federal police are involved...," he wrote. "Just found out that Melbourne airport has been evacuated =\ and here we are just chilling on the tarmac."

"Now pulled up at a different terminal waiting for buses to come grab us."