Authorities in NSW and Victoria have issued a plea to millions of residents to come clean with contact tracers as both states battle expanding outbreaks.

NSW confirmed six new locally acquired coronavirus infections in the 24 hours to 8pm Wednesday.

The source of two of those infections remains under investigation.

Three are linked to the Lakemba GP cluster, which has grown to 15 infections. All are household contacts of known cases.

Health Minister Brad Hazzard said infected people withholding information from public health officials had been an ongoing issue during the pandemic.

“One of the ongoing problems that public health has had in NSW and also in Victoria is that people are not necessarily telling us the whole truth and nothing but the truth,” Mr Hazzard said.

“Whether it’s deliberate, whether its overlooked, you need to make sure it’s neither of those things.

“Public health officials need to be able to track the chains of transmission and that’s impossible if people don’t give us the full picture of where they’ve been.”

NSW Health Minister Brad Hazzard said health officials needed “nothing but the truth”.

NSW again had more infections than Victoria on Thursday. Victoria reported just six new cases as it tries desperately to put a lid on a surprise outbreak in Shepparton, in the state’s north.

All were in metropolitan Melbourne – a relief for authorities after three positive infections were confirmed in the regional city late on Tuesday.

The COVID-19 outbreak in the town, which is 160 kilometres north of Melbourne, was sparked by a city truck driver who failed to tell contact tracers he had been there.

The man, who was infected as part of the Chadstone Shopping Centre outbreak, visited both Kilmore and Shepparton while infectious on September 30.

He had a worker’s permit allowing him to leave the city. But he also admitted to illegally dining at a Kilmore cafe, where a staff member caught the virus, and told contact tracers he had stopped in Shepparton only after three people in the town tested positive on Tuesday.

Victoria Police confirmed on Thursday morning it would assess whether the man had committed any criminal offences.

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Everyone in Shepparton has been asked to be tested for the virus.

More than 1800 people were tested in the town on Wednesday – compared to an average of about 60. There were widespread reports of queues of up to six hours and centres turning people away because they had reached capacity.

On Thursday, one testing site at Shepparton Sports City reached capacity soon after it opened at 10am, but a second drive-through facility at the same location was due to open from noon.

The Showgrounds test site also quickly reached capacity on Thursday morning.

“I do apologise. We’re working as fast as we can,” DHHS testing boss Jeroen Weimar told ABC Radio.

Premier Daniel Andrews said 2000 more tests were expected on Thursday “after that quite amazing result yesterday”.

“We have got about 400 people in the Shepparton community that are either cases, contacts or their contacts – so those three separate groups of people who are all linked through potential chains of transmission – they are isolated at home and they are isolated at home because of one person,” he said.

“The number of people that can be caught up in different chains of transmission with even just one common element is many, many hundreds of people.”

On Wednesday, Mr Andrews said people who caught the virus would not get into trouble if they gave contact tracers information about everywhere they had been.

“There are infections in Shepparton today that we know of and there is almost certainly going to be more that were all completely preventable if this individual had told the full story,” he said.

Chief health officer Brett Sutton also flagged the possibility of using mobile phone data to trace people’s movements.

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NSW outbreaks investigated

One of the NSW cases under investigation was announced on Wednesday but is included in Thursday’s numbers.

It is a man in his 70s who lives in the Bargo area, south-west. Another of Thursday’s infections is a household contact of that man

The other new case still under investigation lives in south-east Sydney.

There were also five new infections found in returned travellers in hotel quarantine.

On Wednesday NSW Premier Gladys Berejiklian warned the state was on the cusp of a fresh outbreak, similar to the one that began in March at a south-western Sydney hotel that spawned a wave of infections.

“This is the most concerned we’ve been since that first incident when the Victorian citizen came up, infected his colleagues and went for a drink at a hotel,” she said.

“Our state is on the verge of being where it was when we had the first seeding incident from Victoria.”