"I don't have the report with the detail in front of me," he said.
Labor Senator Katy Gallagher was aghast.
"You don't know how many people have passed away and you're now telling me you don't know how many people have the infection?"
"You're the minister for aged care."
Senator Gallagher directed the same question to Senator Colbeck during question time in the Senate on Monday.
Senator Colbeck started his response by apologising to both the loved ones of aged care residents who have died from COVID-19, as well as his colleagues.
"Can I, at the outset, express my sincere condolences to every resident's family who has lost a loved one during the pandemic in aged care [and] to my colleagues, who I have successfully taken the attention off what it should be, which is our efforts to combat the virus," he said.
"I should have had the information ... I take full responsibility for not having that information available to me at the time."
Senator Colbeck said every one of the 335 deaths in aged care settings was "an absolute tragedy".
Last week, Prime Minister Scott Morrison stood by his minister following the blunder. On Monday, he faced pressure from the opposition over it.
"We saw, frankly, a minister appear before the COVID-19 committee who is not up to this task, just not up to it," Labor leader Anthony Albanese told the House of Representatives.
"I don't know what it takes to lose your job on the frontbench of this government."
Labor's deputy Senate leader Kristina Keneally also zeroed in on the minister's knowledge of figures, asking how many coronavirus cases had been linked to Melbourne's Epping Gardens - one of the worst-hit facilities.
Senator Colbeck took the question on notice, before later saying 100 residents, 82 staff and 29 others were connected to the cluster.
Mr Albanese on Monday also repeated assertions made during the royal commission the federal government did not have a specific plan in place to respond to the virus in the aged care sector.
“The fact is there wasn’t a plan, and there wasn’t the action that was required,” Mr Albanese said.
Mr Morrison again rejected assertions his government did not have a plan.
"Where there is an assertion that is made, whether it be before the royal commission, or any other place that asserts something the government has not done when we believe that is not correct, then we will correct that record," he said.
Health Minister Greg Hunt said on Monday more than 448 residents had been transferred from aged care homes to hospitals since a response centre was set up in Victoria last month.
"Yes there has been a tragedy, there is more work to do, but what these people have done is they worked together to potentially save thousands of lives."
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