MELBOURNE - Nearly half the 19 people injured when a driver with no known extremist links plowed into pedestrians in the southern city of Melbourne were foreign nationals, Australian Prime Minister Malcolm Turnbull said on Friday.

Police alleged that the 32-year-old Australian man, a refugee from Afghanistan, had a history of mental illness and drove a car into Christmas shoppers on one of the busiest roads in Australia's second-largest city on Thursday.

The incident was a chilling reminder of attacks using vehicles in cities around the world. Four people were killed in a similar incident in Melbourne in January.

Police said the driver had no known ties to extremist organizations, although they also said he had spoken of the perceived mistreatment of Muslims after his arrest.

They have yet to interview, charge or identify the man.

Turnbull said nine of the victims were foreign nationals. He did not specify their nationalities, but Australian media reported they included people from China, India, Ireland, Italy, New Zealand, South Korea and Venezuela.

"This is a shocking incident to occur just on the eve of Christmas, but we will not be cowed by it," Turnbull told reporters in Sydney.

Four people were killed and more than 20 injured in January when a man deliberately drove into pedestrians just a few hundred meters away from Thursday's attack. That was also not designated as a terror attack.

Canberra has become increasingly worried about homegrown extremism and officials said they have prevented 13 terror attacks on home soil in the past few years.

The government in August unveiled a strategy aimed at preventing vehicle attacks in crowded public places.

Suggested steps include deterrent options like fencing and closed circuit cameras, and delaying approaches with trees and bollards to slow down vehicles.

Police had cordoned off the area immediately after the incident but roads in central Melbourne were open and trams were operating as usual on Friday morning.