Victoria’s coronavirus cases leapt by 21 on Wednesday, in the fourth day of a spike in infection numbers.

Of the new COVID-19 cases, six are from community transmission.

The remaining 15 are in overseas travellers in hotel quarantine. Many of them are people who have recently returned from India, Pakistan and Bangladesh.

Premier Daniel Andrews said that proved the effectiveness of mandatory quarantine for arrivals to Australia – the majority of whom land in Melbourne or Sydney.

“The numbers we are seeing in terms of positive tests in hotel quarantine fully validate the move to that system,” he said.

“It is not surprising, but the most important thing is to have them in hotel quarantine where there is simply no doubt they won’t be mingling in the Victorian community.”

It is the highest number of cases recorded in Victoria since May 4, and brings to 70 the number of active infections in the state.

Five patients are in hospital, two of them in intensive care.

Wednesday also marks the fourth day of higher infection numbers – with nine reported on Sunday, 12 on Monday and nine more on Tuesday.

One of the new confirmed infections is in a contractor at Melbourne’s Stamford Plaza hotel, which is being used to quarantine overseas travellers. An emergency health team has been sent to the hotel.

Another is in a resident of the 53-bed Rosstown Community nursing home in Carnegie, in Melbourne’s inner south-east. The centre is in lockdown after the case was confirmed on Tuesday night.

There is also a new case in a cluster previously linked to Monash Health. It has seven confirmed infections across Melbourne’s south-eastern suburbs.

There is also a confirmed infection in a childcare worker, prompting the closure of the Inspira Early Learning Centre in Gladstone Park, where they work.

The worker attended the centre while infectious for two days last week.

This week’s confirmed cases led to the closure of three Victorian schools after children tested positive.

A grade five student at Strathmore Primary School was one of nine new COVID-19 cases recorded on Tuesday. On Monday, Pakenham Springs Primary School and St Dominic’s Primary School in Broadmeadows were closed after two students at each school tested positive.

All schools were expected to remain closed for 24 hours for deep cleaning and contact tracing.

But Victoria’s deputy chief health officer, Annaliese van Diemen, sought to reassure parents about the risk of community transmission at schools.

“We knew there’d still be cases as the community opened up, we knew that would occur,” she said on Tuesday.

“All of the cases have been students that acquired the illness generally within family situations.”

The four students who tested positive on Monday are part of an extended family cluster that increased by one more case on Tuesday.

A total of 12 people in the family have contracted coronavirus after attending gatherings across five homes in Broadmeadows, Coburg and Pakenham.

-with AAP