The man accused of deliberately plowing into Christmas shoppers on a busy street in the Australian city of Melbourne was charged on Saturday with 18 counts of attempted murder.

The Thursday incident was the second serious vehicle attack in Australia's second biggest city this year.

Police said they had charged the man, former Afghanistan refugee Saeed Noori, after formally interviewing him about the attack that police had earlier described as a "deliberate act."

Police have said Noori, 32, is known to have mental health problems and to use drugs and they did not believe the attack was terrorism-related.

Police suspect Noori was behind the wheel of a white SUV when he deliberately sped up and drove into dozens of pedestrians crossing the road at one of the busiest intersections in Melbourne's central business district.

Noori was to appear in a Magistrates Court later on Saturday.

Islamist militants have used vehicles to attack people several times in Europe and the United States over the past couple of years.

In January, six people were killed in Melbourne's central business district when a man used his vehicle to mow them down. Police also ruled out terrorism for that attack.

Following the January incident, authorities installed 140 concrete bollards in the city center.

Victoria State premier Daniel Andrews said 12 people remained in hospital, including three who in critical condition.

He said there would be an increased police presence at Melbourne events, including the Boxing Day Test Cricket, carols and other major sports events.