* Lockdown for a week starting Thursday night
* 12 new cases reported in Victoria
* More than 10,000 contacts identified (Adds new cases, comments from Victoria acting premier)
By Renju Jose
SYDNEY, May 27 (Reuters) - Australia's second most populous state of Victoria will enter a one-week COVID-19 lockdown forcing its near seven million residents to remain home except for essential business as authorities struggle to contain a highly-infectious outbreak.
From 11:59 pm local time (1359 GMT) on Thursday until June 3, people will only be allowed to leave their homes for essential work, healthcare, grocery shopping, exercise or to take their coronavirus vaccinations.
"We have seen more evidence we're dealing with a highly infectious strain of the virus, a variant of concern, which is running faster than we have ever recorded," Victoria state Acting Premier James Merlino told reporters in Melbourne.
Merlino said contact tracers have identified more than 10,000 primary and secondary contacts who would need to quarantine, test and self isolate, adding "that number will continue to grow and change".
A fresh cluster of infections in Melbourne detected early this week has swelled to 26 on Thursday after the state reported 12 new cases overnight, while the number of virus-exposed sites rose above 150.
The lockdown comes just days after authorities reinstated coronavirus curbs for state capital Melbourne, limiting gathering sizes and making masks mandatory in restaurants, hotels and other indoor locations until June 4.
Officials have traced the latest cluster, the first in the state in more than three months, back to an overseas traveller infected with a variant first found in India, although the virus transmission path is still unclear.
The unnamed Victoria man tested negative after finishing his quarantine in neighbouring South Australia and flew to Melbourne this month but tested positive six days after he arrived.
Victoria endured one of the world's strictest and longest lockdowns last year to suppress a second wave of COVID-19 that killed more than 800 people in the state, amounting for 90% of Australia's total deaths since the pandemic began.
Swift contact tracing, snap lockdowns and strict social distancing rules have helped Australia keep its COVID-19 numbers relatively low, with just over 30,000 cases and 910 deaths. (Reporting by Renju Jose; Editing by Karishma Singh and Michael Perry)
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