Sydney: Australian Prime Minister Malcolm Turnbull on Friday said the car attack incident on Thursday in Melbourne was not a terrorist act, although the suspect claimed to have acted due to mistreatment of Muslims.

The driver of the vehicle, a 32-year-old Australian citizen of Afghan descent who has not yet been officially interrogated, has a history of "serious mental illness and drug abuse," Turnbull said in a press conference, Efe news reported.

Turnbull labelled the act "despicable and cowardly" but said it was "an isolated incident" as the suspect had no links to "any political issues or extremist groups." The Prime Minister further assured that the government still has not ruled anything out.

"Terrorism is politically motivated violence. At this stage, the police are not satisfied they can describe it as that, although he has made reference to the perceived mistreatment of Muslims, as a justification for his actions," Turnbull said.

He also confirmed that 19 people were injured in the incident, 12 of whom still remain in hospital, and three are in critical condition.

Among the injured are nine foreigners, including a Chinese, an Indian and a four-year-old New Zealander with head injuries.

After the incident, police arrested a second suspect, a 24-year-old man who was reportedly recording the event and carrying several knives in his backpack but the authorities believe he has no connection with the incident.