Victoria has recorded its highest number of coronavirus cases since the outbreak of the pandemic, with 75 new confirmed infections.

Health Minister Jenny Mikakos said on Monday the cases were “overwhelmingly” concentrated in the northern and western suburbs of Melbourne, but the risk remained for the entire state.

She urged all Victorians to “remain vigilant” as the state recorded its highest number of infections since March.

“Obviously we are concerned by the increasing number and the upward trend and we are monitoring the situation very closely,” she said.

Just a week ago, there were 16 new cases – making Monday’s latest result a five-fold increase that also represents a record number of locally acquired cases.

The state had a net increase of 71 cases on Monday (with four cases reclassified). Its death toll remains at 20 and nine people in hospital. It has had a total of 2099 COVID-19 infections.

The breakdown of Monday’s infections is:

• One in hotel quarantine;
• 14 linked to outbreaks;
• 37 were detected through routine testing;
• 23 are still under investigation.

Ms Mikakos said six new cases were believed to be from community transmission, taking that to 271, with 288 active cases.

“There’s a number … that are still to be determined whether there is a link between new cases and known outbreaks and we believe that those numbers may well increase during the course of the day.

“There is now a link that has been established between the North Melbourne family outbreak and the Brimbank family outbreak. Four of the new cases have been linked to this outbreak,” she said.

Chief health officer Brett Sutton said the number was concerning. He again urged people to stay at home and get tested if they felt unwell.

“I think it will get worse before it gets better. It is a concerning number. But it is very hard to make reductions in this space,” he said.

“That means [a] runny nose, sore throat, fever, whatever the symptoms are, stay-at-home, get your test, don’t interact with other people until you have that test result back and you are well.”

At the weekend, Victoria recorded 90 new cases of the virus (41 on Saturday and 49 on Sunday), and has had a double-digit increase for 12 days running.

The majority of the weekend’s cases were locally acquired.

The latest figures contrast with Western Australia, which had one new case. NSW reported seven new cases on Monday, but all were in hotel quarantine from return travellers.

Queensland had no new cases.

The latest numbers come as a year eight student from St Bernard’s College in Essendon tested positive to COVID-19. The school is closed due to school holidays and will have a deep clean in coming days.

Earlier, Professor Sutton said Victoria was “right at the edge” of being able to control its second wave of the virus.

“It’s absolutely a second peak and it’s going to challenge us in the same way as that first one. But like the first one, but we have been testing as significantly as at any point in Australia,” he said.

“It’s an genuine challenge now. I think we’re right at the edge, in terms of being able to manage it.”

Later, Professor Sutton said the “clearly big numbers today” were “absolutely concerning”.

“The effective reproduction number has come down, but it is not below one. It needs to be below one in order to drive numbers down,” he said.

“When you have got a number of outbreaks, it really doesn’t matter what your R is. You have 75 new opportunity for transmission to others.”

Health authorities will await the outcome of the 10-day testing blitz in hotspot suburbs before deciding on further restrictions or lockdowns in targeted communities. Professor Sutton described the idea of locking down individual suburbs as “a balancing act”.

“We don’t want to drive people out of suburban areas into new unaffected areas. So there is a balancing act in terms of making the call on a lockdown,” he said.

“We know that it is a real challenge for businesses, it is a real challenge for people in their homes, if that is what is required. But it is absolutely an option.”

-with agencies