SYDNEY (BLOOMBERG) - Concerns in Australia about Covid-19 spreading in quarantine are mounting as three new cases among a family of returned travellers were discovered to have been transmitted in a Sydney hotel.

The infections, initially recorded as contracted overseas, are now believed to have been picked up from a family of four in an adjoining room in a city quarantine hotel, New South Wales Health said in a statement on Sunday (April 18). Investigations into how the transmission occurred are under way, it said.

"All guests staying on the same floor of the hotel have been retested and (these have) returned negative results," and staff who worked nearby are self-isolating and getting tests, New South Wales Health said.

The incident adds to debate over possible shortcomings within the hotel quarantine system, given the rise of more infectious strains of the virus. The new cases also fuel speculation that ventilation systems may be contributing to dispersion of virus.

Shadow Minister for Health and Ageing Mark Butler on Sunday called for national standards on quarantine and for dedicated facilities to be established away from the central business districts. Federal and state leaders will meet to strategise on the response to the virus and the vaccine roll-out on Monday.

The total number of cases in New South Wales since the start of the pandemic stands at 5,187.