Health Department officials told a Senate committee hearing that although the app is working and collecting data, state and territory governments were yet to sign agreements ensuring the privacy and security of the information.

Acting health department secretary Caroline Edwards said the agreements were provided to state and territory agencies late Sunday and early Monday and the Office of the Australian Information Commissioner was also being consulted.

Ms Edwards said she expected the agreements to be in place by the end of this week.

The hearing was told that as of midday Wednesday 5.1 million people had registered to use the app, which cost $1.5 million to develop. Prime Minister Scott Morrison has made its widespread use one of the factors National Cabinet will consider in deciding on the relaxation of social distancing restrictions at its meeting on Friday.

The government has faced tough questioning over data privacy and security measures in the app and on Monday released draft legislation setting out stiff penalties of up to five years imprisonment for unauthorised data access or trying to compel people to download the app.

Attorney-General's Department deputy secretary Sarah Chidgey told the hearing that the extent of privacy protections provided for the app were "unprecedented".

Ms Edwards said the government had taken the "very unusual" step to exclude access to app data by law enforcement agencies.

The Health Department has also refuted claims that state territory officials will not need to personally identify themselves to access the app data.

A department spokesman said strong access management systems had been put in place which included an audit trail to show the actions of individual users.

But senators grilled department officials on the selection of Amazon Web Services to manage the central data store amid concerns the data could be accessed under US cloud computing laws.

Officials said the data would be stored in Australia and subject to Australian law and Ms Chidgey said the possibility it could be accessed by US law enforcement agencies was "remote".

University of Sydney cybersecurity expert Suranga Seneviratne said he was satisfied with the app's security safeguards and had downloaded it.

"I think it is sufficiently secure in the sense that it collects only minimal information," he said, though he urged the government to release the app's source code.

Digital Transformation Agency chief executive officer Randall Brugeaud told the committee hearing the code would be released late this week or early next week.

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He added that problems in the way the app's Bluetooth access was managed by Apple smart phone operating systems were likely to be rectified within the next two weeks as Apple and Google collaborated on a solution.

The committee heard there was a "variability" in how well the app worked in connecting with other phones, particularly in Apple devices, where older phones running older operating systems, and phones where the app is running in the background.

The problems with effectiveness were only present in Apple phones and not Android phones, officials said.

Nationals Senator Perrin Davey also sought assurance that the app would still be effective in rural and remote areas where there is little or no phone reception, and was told the app would still work and detect other phones if it was out of range.

Prime Minister Scott Morrison has previously said the app would be most effective if it was downloaded by at least 40 per cent of the Australian adult population, but Ms Edwards said the department hadn't provided advice that was the case or modelling around that figure.

Labor Senator Murray Watt asked why Mr Morrison had said restrictions would be lifted once the app got to 40 per cent of people, but Ms Edwards said that figure wasn't based on advice from the department.

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