Chief Health Officer Jeannette Young today ordered the south-east Queensland lockdown be extended to 4pm Sunday. But it may go beyond that, unless the restrictions, and a higher rate of testing, do not slow the spread of COVID-19.

Young warned the outbreak was “escalating” – there was one case on Friday, six on Saturday, and nine on Sunday – and contact-tracers were struggling to make connections.

“We need to lock down really, really hard, the hardest we’ve ever locked down,” Young said, noting that there were still too many people driving into the CBD.

“I cannot understand how anyone would be in an office today. If you are in an office today, why aren’t you home?”

There were 13 new cases confirmed overnight, linked to Ironside State School, and a karate school held there, taking the total to 31 and growing. One of the new cases was already in home quarantine, and tested positive before other family members, while, worryingly, another had been in the community for six days while infectious.

Young said the Delta variant was spreading among young people who were “spared” during previous outbreaks, and with masks not required in schools before now. Ten of the newly announced cases were in children aged under 10.

“I really am very, very concerned about these six schools,” Young said, noting children had already carried the virus into households.

“We know Delta is much more likely to spread among younger people.”

Schools will move to remote learning and Brisbane’s annual show, the Ekka, has been cancelled for the second year in a row. Police are enforcing the lockdown restrictions – they turned out to an anti-lockdown protest this morning – and have arrested people refusing to comply.

“We know that you need a person to move this virus,” Young said.

“So, if everyone stays home, we won’t be moving this virus around.”

Young acknowledged the disruption it would have and said staff having to home quarantine was also “destroying our health workforce numbers”.

As more testing sites are brought online, or online for longer, hospitals are having to restrict activities in order to focus on the outbreak and deal with staffing shortages. That will see elective surgery postponed.

Young revealed the Queensland Children’s Hospital was on standby to treat any young people whose illness deteriorates, in addition to four dedicated COVID-19 hospitals in the south-east.

Queensland Health is still playing catchup to identify how the virus has spread. Genomic sequencing suggests it originated in one of two overseas travellers who arrived on June 29, but while a medical student was believed to have introduced the virus to an Indooroopilly household, Young said it appeared someone from the household gave it to the student. How the virus made it to the household, and Indooroopilly State High School, remains unknown.

Young had thought one of the travellers, who returned home to the Sunshine Coast, may have inadvertently set off a chain of transmission. However, test results suggest that traveller did not infect any family members, making Young doubt her original theory until more information comes to hand.

One of the Brisbane people caught up in the outbreak had travelled to Rockhampton while infectious, putting central Queensland on alert. Young wants people outside south-east Queensland to get tested if they have symptoms “because I don’t know where this virus has already moved to”.

While Young repeatedly urged people aged 60 and over to get vaccinated, with AstraZeneca still in good supply, she stood by her cautious stance on its use by young people. Due to the higher risk of blood clots, younger people should consult their GP, she said, having previously urged them to wait for Pfizer if possible.

“I said I didn’t want 18-year-olds to have AstraZeneca and I still don’t,” Young said today.

“Even now.”

Young acknowledged teenagers were being vaccinated in NSW but said she was focussed on older people who were more at risk of dying.

Deputy Premier Steven Miles told ABC Radio “we’d love to have more vaccine and we’d love to see more people vaccinated but we’re not going to give people a vaccine that’s not recommended to them”.

The 21,085 tests done over the last 24 hours was about half what Young wanted. There are now 64 drive-through testing clinics in south-east Queensland and private pathologists have agreed to do tests without a doctor’s referral until Friday.

Supermarkets have asked the government to reassure Queenslanders there will still be supplies available after reports of panic buying.