Canberra’s lockdown will be extended until midnight on September 17 as its coronavirus outbreak continues to grow.

ACT Chief Minister Andrew Barr said the lockdown had proven effective but it was essential to keep it going to reduce the outbreak.

“It is a slow process and it will take more time,” Mr Barr said on Tuesday.

“We still have unlinked cases in the community.”

There will be some changes to lockdown settings in the national capital from this Thursday.

Another 13 cases were reported on Tuesday, with seven linked to exposure sites. Six are under investigation.

It takes the total number of active cases in the ACT to 242.

Four of the cases were in quarantine for their entire infectious period.

At least eight people were infectious in the community, with the remaining case still under investigation.

“Any ongoing chains of transmission or cases with an unconfirmed source contributes to increased risk to our community,” Mr Barr said.

“Considering this, and in addition to the continuing situation in NSW, which surrounds us, and several clusters that we’ve talked about in our vulnerable and high-risk settings, the best decision is to extend the lockdown.”

Thirteen people are in hospital with three in intensive care.

-with AAP