Four new cases of Covid-19 have been identified in Melbourne’s northern suburbs, Health Minister Martin Foley says.

Three of them are close family contacts of the initial case, whose source of infection remains unknown.

The first case was a man who showed symptoms of the coronavirus on 20 May. He got tested two days later on 23 May.

A male relative went with him when he got tested, and that person – who was not showing symptoms – had also tested positive, Foley said.

Both live in Whittlesea, in Melbourne’s outer north.

Two other relatives, a woman and a preschool-aged child, were also tested and returned positive results.

All were close contacts of the first case and lived in two different households.

Two new Tier 1 exposure sites have been listed.

They include the Jump Swim School in Bundoora between 8.55am and 10.15am on 21 May and Highpoint Shopping Centre between 5pm and 8pm on 20 May.

Anyone who attended the school or shopping centre at those times was asked to get tested and isolate for 14 days.