The lockdown will remain in place for at least seven days until October 5.

Stay-at-home orders will also apply to people who have been in the Muswellbrook and Port Macquarie LGAs since September 22 and September 17 respectively.

All residents in these LGAs must remain at home unless it is for an approved essential reason.

Essential reasons for leaving home include shopping for food, medical care, receiving a COVID vaccination, exercise compassionate needs or essential work and tertiary education which can't be done from home.

State member for Upper Hunter Dave Layzell said he had been briefed by NSW Health Minister Brad Hazzard and NSW Chief Health Officer Dr Kerry Chant about the risk posed to the community resulting from an unvaccinated and highly infectious individual.

"The investigation by the HNE Public Health Unit highlighted a number of potential COVID exposures to the community," Mr Layzell said in a statement.

"As a result of this advice, I endorsed their advice to support a snap seven day lockdown. This has been accepted by the Crisis Cabinet.

Mr Layzell said the Muswellbrook LGA did not have adequate levels of vaccination in the community to remain open safely.

"Using the current trends, within four weeks our double dose vaccination rates should be over 70 per cent but until then, we are still living with the threat of a serious outbreak," Mr Layzell said.

"I acknowledge the impact this decision will have on small business and peoples lives. The pandemic is a very challenging time and the path to recovery will undoubtedly have many bumps along the way."

Muswellbrook Shire Council will assist Hunter New England Health in operating a drive-through COVID testing clinic at the Muswellbrook Showgrounds from Wednesday, September 29 until Tuesday, October 5.

The testing clinic will operate daily from 7:30am to 2:30pm with entry to the clinic from Maitland Street.