* New South Wales reports 163 new local cases

* Australia to send 50,000 extra Pfizer doses to Sydney

* Thousands protest against lockdown in Sydney

* Victoria logs 12 new local cases in encouraging trend (Adds NSW minister comments on anti-lockdown protest; protests in other states)

By Sonali Paul

MELBOURNE, July 24 (Reuters) - Sydney will get 50,000 more doses of the Pfizer vaccine this week to battle its worsening COVID outbreak, Canberra said on Saturday, reversing a rebuff by the Australian government and other states the previous day of a plea for more supplies.

Australia reported 176 new locally acquired COVID cases on Saturday, a third consecutive daily record with nearly all cases in the state of New South Wales, centred in the country's largest city, Sydney.

Officials fear the outbreak could jeopardise the rest of the country.

Defying a statewide stay-at-home order, however, 3,500 mostly maskless protesters clashed with police in downtown Sydney, decrying a month-long lockdown in what the state police minister said was the best case study of a superspreader event since the start of the pandemic.

"You don't have to be an epidemiologist to work out that if this is a superspreader event, we can forget about lifting restrictions next week," New South Wales Police Minister David Elliott told reporters.

Police arrested 57 people with more under investigation, facing hefty fines and penalties.

There were protests in Melbourne and Adelaide, also under lockdown, and in Brisbane, where there are no restrictions. Police arrested six people in Melbourne, including one for assaulting an emergency worker, and fined dozens of others for failing to comply with orders to stay within 5 km of home.

New South Wales Health Minister Brad Hazzard stressed the state's urgent need for extra vaccine supply, adding that with so many people flouting the stay-at-home orders it was the only way to stop transmission of the virus.

"At the moment it's like fighting a war with both arms behind your back," he told reporters.

New South Wales reported 163 locally acquired cases of COVID-19 on Saturday, up from 136 the previous day, with 37 patients in intensive care.

Hazzard renewed a call for other states to give up some Pfizer vaccines so that younger people in Sydney's hotspots could be vaccinated, reminding neighbouring states about the help New South Wales had provided during other crises.

"I can't quite see the difference between beating back fires and beating back ... floods and beating back this COVID virus that could actually, if it gets worse here in New South Wales, could actually create massive problems for the whole country," he said.