The plea comes after genomic testing showed a security guard who worked at the Sofitel hotel in Sydney on March 6 had the same highly-contagious UK strain of the virus as a returned traveller at the hotel.

The case ends NSW’s 55-day run with no community cases and comes just one day after all of Australia’s interstate borders were fully opened for the first time in almost a year.

Health authorities are trying to work out the source of the man’s infection, as the infectious traveller did not open his hotel room door nor leave his room while the guard was on shift.

NSW Chief Health Officer Kerry Chant said authorities had reviewed CCTV footage from the night the guard worked.

The guard – who has already received his first dose of the Pfizer vaccine – had no symptoms and had followed the required protocols, Chant said.

“We haven’t been able to find an exact source, an explanation for how this person became infected,” Chant told reporters on Monday.

“We are testing everyone who worked, co-workers who worked with this gentleman to just check there is not someone else who may have been an intermediary that transmitted to this gentleman.”

Quarantine has been extended for those staying on the 11th floor of the hotel, while 167 staff who worked at the Mantra Hotel in Sydney where the man worked an overnight shift on March 12 have also been contacted.

Berejiklian said that while every community transmission caused “sleepless nights”, there was no need for premiers to “overreact” to the latest case.

She urged state governments across Australia to “give us a chance to demonstrate our capacity to get on top of this” and show how the vaccine rollout is working.

“There is no evidence of widespread transmission,” Berejiklian said.

“(It) dashes confidence everywhere if people can’t rely on borders staying open.

“I’m not suggesting there is no risk, there always is, but … please assess the risk against the facts, and at the moment there is one case of a guard.”

-with AAP