An extraordinary hearing of the inquiry was called on Tuesday after the Department of Health and Human Services handed over a number of emails it had not originally tendered.

The department's lawyers said they did not consider them critical or relevant.

But counsel assisting the inquiry Tony Neal QC said the emails cover "matters that occupied a very considerable amount of the board's time" during the inquiry.

"You may consider it adds some weight in one direction or another to your deliberations as to who was in charge for the detention regime," Mr Neal told retired judge and inquiry head Jennifer Coate.

One email chain, which begins on March 30 and ends on July 2, involves a number of senior DHHS officials, including Finn Romanes, the then-Deputy Public Health Commander.

An email written by Dr Romanes titled "Information - Chain of Command - people in detention" was described by Mr Neal as "most significant".

It lists Professor Sutton as the head of "all policy and oversight of people in detention".

A second email chain on March 27 involves a number of DHHS staff, including Prof Sutton, and a Commonwealth official.

The official asks what security arrangements will be in place at Victoria's quarantine hotels.

Prof Sutton is copied into a reply which reads: "Private security has been contracted to provide security at the hotels with escalation arrangements to Vic Pol as needed".

He acknowledges he has seen the email by replying "Thanks so much" to its author.

Prof Sutton had told the inquiry in September he was not aware of guards being used in the program until a COVID-19 outbreak at the Rydges on Swanston in late May.

"As a result of this new material, those assisting you are in the process of seeking a response, in the form of an affidavit, from Prof Sutton to specific questions posed by the board and focusing on these emails," Mr Neal said.

He said Prof Sutton had seven days to provide his explanation.

When asked about the emails at the weekend, Prof Sutton told reporters he had received up to 30,000 emails since the start of the pandemic.

"I get up to 150 a day ... If I have missed a reference to security in late March when the program was established, I'm sorry," he said.

Victoria's hotel quarantine program was established within 36 hours of a national cabinet meeting on March 27.

Former Victoria Police Chief Commissioner Graham Ashton told the inquiry he learnt private security would be used in the program sometime between 1.16pm and 1.22pm on March 27, but couldn't recall who told him.

Phone records established Department of Premier and Cabinet secretary Chris Eccles spoke to Mr Ashton at 1.17pm.

Mr Eccles resigned after the revelation, though he emphatically denied he spoke to Mr Ashton about security.

Since obtaining this information, Mr Neal said the inquiry has "requested certain parties to provide further answers on affidavit to questions directed to the issue of the decision to engage private security contractors".

More documents have also been requested.

Outbreaks among security and hotel staff at Rydges and Stamford Plaza have been blamed for 99 per cent of Victoria's COVID-19 second wave cases.

More than 18,000 people have been infected and 800 have died.

The $6 million inquiry is due to hand down its final report on November 6, but Ms Coate said the new evidence could "unsettle" the deadline.

"As soon as I am in receipt of the outstanding material, if the report date is affected and needs to be extended, I will advise the premier and seek any necessary extension," she said.

Australian Associated Press