"An investigation into how COVID-19 transmission occurred between returned travellers who had been in quarantine at the Mercure Hotel has led NSW Health to reclassify one case, previously reported as overseas acquired, as locally acquired," it said in a statement on Tuesday.

Of the three returned travellers, two were family members and stayed in connecting rooms at the Mercure between April 7 and April 12.

The third traveller, whose case has been been reclassified as locally acquired, stayed in an adjacent room.

All three people share the same viral sequence for the B1.351 variant of concern, first identified in South Africa.

The investigation did not identify any further cases of transmission.

Meanwhile, as Perth and Peel's three-day lockdown ended on Tuesday, anyone who travelled there and visited any venues of concern are required to self-isolate.

Others who have been in WA but not visited any of the nominated venues no longer need to stay home but people arriving from WA must complete a declaration form on the Service NSW website and confirm they have not attended a venue of concern.

NSW recorded no new locally acquired cases of COVID-19 in the 24 hours to 8pm on Monday.

Australian Associated Press