NSW Ag Minister Adam Marshall announced on Thursday morning that he had COVID-19.

He said he had been in isolation in Sydney since late Tuesday night when he found out he was a close contact of a case on Monday night. Mr Marshall urged everyone to take care.

All MPs who attended Parliament on Tuesday and Wednesday were ordered into isolation after Mr Marshall tested positive, including Mr Saunders.

The Dubbo MP had a COVID test on Thursday and at the time of publication was still awaiting the result.

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There were 18 new locally acquired cases of COVID-19 in NSW to 8pm on Wednesday night, however, 13 of them had already been announced.

NSW Premier Gladys Berejiklian - who confirmed she had received a negative COVID test - said it was the "scariest period" NSW had faced since the start of the pandemic.

"My level of concern is medium to high," she said.

"But of the new cases today, all but one is linked. We expect more new cases in the coming days.

"This is a very contagious variant but at the same time we are at this stage comfortable that the settings that are in place are the appropriate settings, but that is so long as everybody does the right thing."

Ms Berejiklian said at this stage a lockdown wasn't necessary.

Even after being informed his COVID test was negative, Mr Donato said he would continue to isolate as a matter of precaution.

"I was relieved to get the negative test result, definitely, but we are still waiting on advice. There's a handful of us that aren't certain as to what happens next, but I will be staying here in Sydney regardless," he told ACM on Thursday afternoon.

"Although I've tested negative now, I could become symptomatic in the next few days so I think being cautious is the right way forward without having received a Public Health Order yet, it's a rapidly changing situation.

"They could lock us down soon in Sydney, we just don't know, but I've spoken to my wife and I don't want to put her or anyone else at risk."

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