South Australia is increasing COVID-19 testing along the Victorian border amid threats of a blockade by truckies angry over new essential worker rules.

The Transport Workers’ Union says it’s unrealistic to require essential workers crossing the border to have a virus test within 24 hours, which could leave some truckies needing to get tested every day.

State secretary Ian Smith said some freight drivers were already refusing to come into SA and Victorian truckies were threatening a blockade to prevent the supply of food.

“We understand the current circumstances are ever-changing but in order to achieve a relatively undisrupted transport industry there needs to be flexibility, not only from essential workers but also the state government,” Mr Smith said.

Premier Steven Marshall said the government had already moved to “massively” increase testing at the border and officials would meet with truckies in the next 24 to 48 hours.

“Our truckies have kept Australia moving during this coronavirus and we’re grateful for that,” Mr Marshall told reporters on Saturday.

But the premier said the new border rules were “absolutely necessary”.

“When we’ve had to put these in place previously, we’ve lifted them as soon as we practically can,” he said.

“We’re seeing a deterioration of the situation in Victoria. We’ve got to protect ourselves at the moment.”

Mr Marshall said there was also a direction in place now which allowed truck drivers to come in with proof of a negative test result in the previous 48 hours.

SA reported no new local virus cases on Saturday despite having several hundred people in quarantine over their links to potential exposure sites both in South Australia and Victoria.

All have returned negative virus tests so far, something the premier said was a “positive result for us here in South Australia”.

Mr Marshall said it was “miraculous” that a family who relocated from Sydney and spent five hours with virus-infected removalists had still not come down with the disease.

“We’re asking those people to stay in directed home isolation for 14 days because we know there is an incubation period so we’re not out of the woods yet,” the premier said.

“But the early results are extremely good for South Australia. I think we’ve dodged a bullet.”