The greater Sydney lockdown will be extended by a week, after NSW confirmed 27 more local coronavirus cases on Wednesday.

State health authorities have also moved their focus to three Sydney local government areas – Fairfield, Canterbury-Bankstown and Liverpool – where “concerning statistics” have emerged.

Residents of those areas are particularly asked to limit their movements in coming days.

“Can I say to the communities in those area – many have a similar background to me – please don’t mingle with family,” Premier Gladys Berejiklian said on Wednesday.

“The NSW government doesn’t want to go to the next stage but we are even considering if there are any further actions we need to take in those three local government areas.”

She confirmed the “difficult decision” to extend the lockdown of greater Sydney, Wollongong, Shellharbour, the Central Coast and the Blue Mountains, saying the Delta strain of the virus that has now infected more than 350 people in NSW had been a “game-changer”.

“It is extremely transmissible and more contagious than any other form of the virus that we’ve seen,” Ms Berejiklian said.

“We don’t want to be in a situation where we are constantly having to move between lockdown, no lockdown, lockdown, no lockdown. What we want to do is give us our best chance of making sure this is the only lockdown we have until the vast majority of our citizens are vaccinated.”

Tweet from @NSWHealth

Of Wednesday’s new COVID cases, only 13 were already in isolation throughout their infectious period. Seven were active in the community, while the remainder were isolated for part of that time.

“They are the numbers we are looking at when it comes to determining the length of the lockdown,” Ms Berejiklian said.

“That is why the NSW government, based on the health advice, which is our key indicator, made the difficult decision to announce the extension of the lockdown and the existing restrictions in the regions for one week further until Friday midnight, 16 July.”

Schools outside greater Sydney will resume face-to-face learning from next week. But there will be remote learning for those still under stay-at-home orders.

‘[It] is not because schools aren’t a safe place, they are a safe place, but what we really need to do in greater Sydney is reduce mobility,” Ms Berejiklian said.

She said most virus cases emerging in Sydney’s south-east were now in isolation. But that wasn’t the case in Fairfield, Canterbury-Bankstown and Liverpool.

“We have seen overnight some concerning statistics on what is happening in the Fairfield, Canterbury-Bankstown and Liverpool council areas,” Ms Berejiklian said.

“You might think you are doing the right thing by visiting loved ones, you might think you are doing the right thing by babysitting others’ children or whatever but the key message in [those] local government areas is please do not leave the house.

“We just need everybody to please follow the health orders.”

New cases on Wednesday included another worker and a resident at the SummitCare nursing home at Baulkham Hills. The worker has had a Pfizer dose while the resident is fully vaccinated.

There are now 10 infections in the SummitCare cluster.

There are also three more cases linked to the illegal party at the Meriton Suites Waterloo on Saturday, June 26. That outbreak has risen to 15 – seven people who attended and eight household contacts.

There are also two cases linked to the Commonwealth Bank in Roselands Shopping Centre, in Sydney’s south-west. It has been listed as an exposure centre for June 28-30, and anyone who was there on those days must get tested and isolate for 14 days, regardless of the result.

NSW has 37 COVID-19 patients being treated in hospital. That includes seven in intensive care, two of whom require ventilation.

Chief health officer Kerry Chant said 14 of the hospital patients were aged under 55, “which should dispel the myth that this is something that only impacts on the elderly”.

“Of the seven people in ICU, one is in their 30s – a bit of a wake-up call to young people,” she said.

One of the NSW ICU patients is in their 50s, two are in their 60s and three are in their 70s.