The snap lockdown, announced last Thursday and introduced on Friday, will now go until at least September 2.
Chief Minister Andrew Barr said the number of new cases recorded over the last 24 hours was "concerning".
"It demonstrates that the virus is active in the community," he said.
"There are now thousands of close contacts and a growing list of exposure sites.
"This is a serious situation.
"We do not want to see the numbers continue to grow, and we do not want to see exponential growth as we have seen in other jurisdictions.
"Please stay at home."
There are now 28 active cases in the territory.
Mr Barr thanked the 5723 people who had come forward to get tested.
The ACT's chief health officer Kerryn Coleman said the increase in cases was expected but is still very high. None of the cases are in hospital.
Aged care worker among new ACT cases
Among today's new cases is a worker at the Greenway Views Village aged care home, which was locked down overnight.
Initial investigations suggest the employee worked three shifts while "unknowingly infectious".
All residents and staff will be tested today.
"This is the first time that the ACT has actually recorded a case in a retirement village or a residential aged care facility," Dr Coleman said.
On Friday, the ACT entered a snap seven-day lockdown after the first positive case in the Territory in more than a year.
It is the first time the ACT has been under a lockdown of this nature since the early days of the pandemic.