Mr Pezzullo made the concession during a Senate estimates hearing on Monday afternoon, effectively admitting it was possible the deportation fiasco involving the men's world number one tennis player could have been averted had the long-promised system been in place.

The new digital passenger declaration system, which will record passenger details and capture and verify their vaccination status, will finally go live on Tuesday following repeated delays.

However, the system will not be fully complete until June.

Passengers will fill out their online declaration up to 72 hours prior to travel, providing border officials with immediate access to their travel documents.

The real-time access would mean officials would able to check if a traveller had the correct documents to enter the country - including proof of vaccination or a medical exemption - before they boarded a flight to Australia.

Mr Pezzullo confirmed that the new system would alert authorities to travellers who were planning to board flights to Australia without the proper documents.

If an unvaccinated person who didn't have a place in quarantine in Australia tried to board a flight, the plane wouldn't be allowed to take off, Mr Pezzullo said.

Labor's home affairs spokeswoman Senator Kristina Keneally asked Mr Pezzullo if it was possible that had the new system already been in place, Djokovic would have been barred from flying to Australia in early January.

Mr Pezzullo conceded it was.

"With real-time interrogation, not just of his declaration but of his supporting documents, it is hypothetically possible, yes," he told the hearing.

Djokovic was allowed to board a flight to Australia, but his visa was cancelled upon arrival in Melbourne when he was unable to produce evidence to support a medical exemption to vaccination requirements.

The Serbian tennis star had been granted an exemption to compete in the Australian Open under a separate process overseen by Tennis Australia and the Victorian government, which led him to believe he was free to enter the country.

The visa cancellation decision was overturned in court on procedural fairness grounds, before Immigration Minister Alex Hawke intervened and deported the 20-time grand slam champion.

The new digital system was expected to be up and running by July last year, and then by November, according to ministerial briefings referenced by senator Keneally during Monday's hearing.

Asked to explain the delay, Mr Pezzullo said funding had not been allocated until June last year.

Following Mr Pezzullo's evidence, senator Keneally accused the Morrison government of incompetence.

"The Morrison government announced the digital passenger declaration in October 2020," she said. "They promised it would be here in July 2021. Then they said it would be here in November 2021. Then they said it would be here in December 2021.

"Labor will be taking no lectures from this incompetent Liberal mob that couldn't even stop one tennis player at the Australian border without creating international embarrassment for our country and the Australian Open."

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