Australian authorities said Friday they've detected the highly contagious Delta variant of COVID-19 in Melbourne.
It's sparking concerns of an incoming spike in cases.
The Delta variant, which likely caused the outbreak in India, is one of four more contagious variants classified by the World Health Organization.
It was detected in two family members who travelled from Victoria state to neighbouring New South Wales two weeks ago while likely infectious, and visited several popular tourist locations there.
Victoria's Chief Health Officer Brett Sutton said Friday it was possible the two had contracted the virus in New South Wales, but more tests would be needed.
"It's obviously a concern that it is not linked to other cases but we are absolutely, as we have done for the Melbourne cluster, chasing down all of those primary-close contacts for this family and looking into where it might have been acquired."
New South Wales has not reported any local cases in a month.
Meanwhile Victoria, Australia's second-most populous state after New South Wales, is battling to contain its latest outbreak after more than three months of no cases.
The government has linked all the cases to a single traveler released from quarantine after testing negative.
Melbourne is in its second week of hard lockdown, which authorities have blamed on the spread of the Kappa variant, also first detected in India.
Snap lockdowns, regional border restrictions and strict social distancing rules have helped Australia contain prior COVID-19 outbreaks.