The Bondi COVID-19 cluster has risen to 21 after NSW Health authorities announced 10 new infections since Monday.

Seven of the infections were detected outside of the reporting period and will be included in tomorrow’s figures. Five cases were recorded before the 8:00pm reporting cut-off, although two of those were confirmed yesterday.

NSW Chief Health Officer Kerry Chant says concerns remain over the extreme transmissibility of the Delta strain of the illness.

“In some instances, the exchanges have been scaringly fleeting,” NSW premier Gladys Berejiklian said.

“People not even physically touching each other but literally fleetingly coming into the same airspace has seen the virus transferred from one person to another.”

Dr Chant said the contagious nature of the virus means the state is at a critical stage in managing the outbreak.

Hundreds of people are isolating after scores of exposure sites were identified across more than a dozen suburbs.

Passengers on three busy bus routes – visiting Baulkham Hills, Sydney, Northmead, Parramatta, Winston Hills, Haymarket and Newtown – were listed as close or casual contacts.

“From one person alone we’ve had four or five cases … even if they infect one or two each, you can see how it grows exponentially.”

“We need to find all the cases, and make sure we identify the close contacts and casual contacts.”

As a result, mask-use has been mandated in a number of settings across the seven local government areas, and on public transport in Greater Sydney, Wollongong and the Shellharbour region.

Queensland has recorded one new locally acquired case of COVID-19 linked to a woman who tested positive for the virus at the weekend after undergoing hotel quarantine. The man in his 60s visited the Portuguese Family Centre at Ellen Grove at the same time as the woman while she was infectious.

“At this stage we’re very comfortable that this person is in home quarantine,” Queensland Premier Annastacia Palaszczuk said.

“We are going to be making sure that we keep a really close eye on all of those people who went to that Portuguese Family Centre, and it’s very important that we monitor them because we don’t want them out in the community.”

Queensland will open its border to Melbourne residents from 1:00am on Friday.

Queensland’s Chief Health Officer Jeannette Young believes the risk stemming from today’s case is low.

There were 36 people at the centre at the time the flight attendant was there, and that cohort is being closely monitored.

Young said the man who was at the Ellen Grove site on Saturday night was contacted on Sunday morning and has been in isolation since then.

Authorities are trying to work out if he was out and about in the community after he was exposed, but the risk is believed to be low.

Young has also revealed preliminary information about how the flight attendant was infected.

A staff member at the quarantine hotel escorted an infected man, who’d arrived from Mongolia, to an ambulance and then went to a higher floor of the hotel and swabbed the flight attendant.

Meanwhile, Queensland’s travel restrictions on Victorians have been lifted, but Queenslanders have been told to reconsider their need to travel to Sydney where there is a cluster of more than 10 cases.