Woolworths at Lanyon Marketplace in Conder is closing three hours earlier until enough staff members can return to work.

The store is closing at 7pm when it is usually open until 10pm. Its deli will also not be staffed.

It's understood as many as 30 to 40 people from the single Woolworths store have had to isolate as a precaution, but Woolworths would not confirm how many staff members had been affected.

"A customer with a confirmed case of Coronavirus (COVID-19) was present in our Woolworths Conder store. Several of our team members are now following advice from ACT Health," a Woolworths spokesperson said.

"As a consequence, we have reduced the trading hours at our Conder store to 7am to 7pm. Customers and team members should be assured they can continue to safely shop and work at our Conder supermarket."

The spokesperson said it was the only Woolworths store in the ACT on reduced hours due to COVID. A Coles spokesperson said none of its stores were on reduced hours.

The confirmed case was present in the Woolworths Conder store on 10 occasions between September 8 and September 22.

It's understood, across Australia, thousands of Woolworths workers have had to isolate after COVID-positive customers entered the stores, but no staff have yet returned a positive result. The spokesperson said COVID-safe procedures were keeping shoppers safe to shop for essentials.