* Australia records 10 deaths in past day, all in Victoria
* Victoria records 459 cases, up from 357 on Saturday
* Court rules against planned protest in Sydney next week (Adds bullet points, comment from health official, daily death count, detail on protest)
MELBOURNE, July 26 (Reuters) - Australia reached a grim milestone on Sunday, recording its highest ever daily tally of deaths from the novel coronavirus, as authorities in Victoria state battled scores of clusters of infection and intensified efforts to trace their contacts.
Victoria's leader, Daniel Andrews, told a media briefing the state had reported 10 COVID-19 deaths in the past 24 hours, Australia's highest ever daily toll.
Victoria also recorded 459 new cases of the coronavirus, its second highest tally ever, he said, falling short only of the 483 last Wednesday, and up from 357 on Saturday, as infections remained persistent despite a two-week lockdown of its biggest city, Melbourne.
The state's second wave is being driven by workplace infections at places like aged-care and healthcare facilities, big distribution centres, slaughterhouses, cold-storage facilities and warehouses, Andrews said.
"What that tells you is that some people ... are feeling sick, they have symptoms and they are still going to work," he said.
"If that continues, then we will just continue to see more and more cases."
The new case tallies came on the day that Victoria carried out the most ever coronavirus tests, at more than 45,000.
Australia has avoided the sort of severe coronavirus outbreaks seen in some other countries, with more than 14,400 cases recorded and 155 deaths.
But authorities are struggling to contain more than 100 clusters in Victoria.
"It is a challenge when you get to these numbers and it is something that would challenge any jurisdiction in Australia which is exactly why we're offering the extensive support we are to Victoria," Deputy Chief Medical Officer Dr Nick Coatsworth told media.
Victoria is under a six-week lockdown with its borders with other states closed and masks mandatory.
Officials have also enlisted the help of Australian Defence Force members, third-year medical students and ambulance workers to focus on tracing contacts of infected people within 24 hours.
"Ten families are currently planning funerals. And the youngest among them have lost someone in their forties. Please wear a mask everyone. And if you don't you will get fined," Andrews said.
The country's most populous state of New South Wales recorded 14 new cases overnight, with almost half connected to an outbreak at a restaurant on the outskirts of Sydney.
Protesters in Sydney vowed to appeal a Supreme Court decision to block a rally planned for Tuesday over the high number of Aboriginal deaths in custody in line with a police request given concerns it could spread the coronavirus. L3N2EX02L