Updated

Melbourne will test a terrorism alarm system this month after police thwarted two alleged plots targeting Christmas-New Year crowds and a lone driver killed six pedestrians in the last year in Australia's second-largest city.

Victoria state Acting Police Chief Commissioner Shane Patton said Monday loudspeakers were being installed at over 90 sites across downtown Melbourne as part of an alarm system to be tested Dec. 28.

Police last month charged a man with preparing to commit a terrorist attack in Melbourne.

Four men are awaiting trial on terrorism charges after being arrested in December last year over a similar alleged plot.

A man has been charged with six counts of murder and 28 of attempted murder after allegedly driving a stolen car along a Melbourne pedestrian mall in January.