By Renju Jose

SYDNEY (Reuters) -The leader of Australia’s New South Wales (NSW) on Wednesday ordered a week-long extension of Sydney’s hard COVID-19 lockdown, warning new cases are bound to rise as the country’s biggest city grapples with the highly infectious Delta variant.

Sydney, home to a fifth of Australia’s 25 million people, was plunged into lockdown on June 26 as a Delta variant outbreak persuaded officials to tighten restrictions in a country that has been slow to vaccinate. Strict stay-at-home orders were due to end on Friday, but now remain in place until July 16.

“This Delta strain is a game-changer, it is extremely transmissible and more contagious than any other form of the virus that we’ve seen,” NSW state Premier Gladys Berejiklian told reporters in Sydney.

With Sydney fighting its worst outbreak of the year so far, total infections have topped 350 since the first case was detected three weeks ago, in its Bondi beach suburb in a limousine driver who transported overseas airline crew.

Berejklian on Wednesday warned Sydney residents she expects cases to rise in the next 24 hours.

A total of 27 new locally acquired cases of COVID-19 were reported on Wednesday in NSW, up from 18 a day earlier. Of the new cases, 20 were either in isolation throughout or for part of their infectious period, while seven cases spent time in the community while they were infectious.

Lockdowns, swift contact tracing and a high community compliance with social distancing rules have helped Australia suppress past outbreaks and keep its COVID-19 numbers relatively low, with just over 30,800 cases and 910 deaths. The current lockdown is Sydney’s second since the pandemic began.

As news of the stay-at-home extension broke, Australian travel-related stocks, like Qantas Airways Ltd, fell in morning trading. Grocery chains Woolworths Group Ltd and Coles Group Ltd – expected by investors to benefit higher sales during lockdowns – were trading about 1% higher, outpacing a slightly higher overall market.

Meanwhile, schools in Sydney will move to remote learning from next week, after ending their southern hemisphere winter break on Friday, to eliminate crowding while parents drop and pick up children.

(Reporting by Renju Jose and Byron Kaye; Editing by Richard Pullin and Kenneth Maxwell)