HONG KONG, June 21 (Reuters) - Legislators in Macau approved a landmark Online Casino bill on Tuesday, the biggest reforms in more than two decades, ahead of an expected casino licence bidding process in the world's biggest gambling hub.

The changes - marking the first major reforms since casinos were first liberalised in 2002 - mean far greater oversight and control by the government into casino operations in Macau.

The vote came as the Chinese special administrative region carries out mass COVID-19 testing of its more than 600,000 population after dozens of locally transmitted cases were found in recent days.

A hotel and Online Casino casino resort on Macau's main peninsula was locked down by authorities on Tuesday due to a coronavirus infection, with some 700 people forced to quarantine.