The ban follows Tuesday's closure of the border between the country's two most populous states because of a spike in COVID-19 cases in Melbourne.
Horse racing continued, initially behind closed doors, throughout Australia's previous lockdowns with horses allowed to move between the two states as long as biosecurity measure were observed.
"Following the increasing confirmed COVID-19 positive cases in Victoria and the continued ongoing developments in that state, Racing NSW has issued the following updated protocols," the body said in a statement on Wednesday.
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"Effective 8 July 2020 Racing NSW has prohibited the transfer of horses from Victoria to any NSW racing stable, licensed premises or racecourse."
Renewed lockdown measures in Melbourne kick in from midnight on Wednesday for at least six weeks, confining around 4.9 million people to their homes except for essential business.
(Reporting by Nick Mulvenney, editing by Editing by Peter Rutherford )
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