The actions of an off duty police officer who arrested the driver of a vehicle that ploughed into pedestrians in Melbourne on Thursday have been described as “heroic”.

The sergeant, whose name has not been released, has been praised by Victoria Police’s acting commissioner Shane Patton after he arrested the 32-year-old driver.

The off-duty cop who detained the driver in Melbourne this afternoon was injured during his incredibly brave act. He’s a genuine hero. #FlidersSt
Thursday’s incident has been described as a “deliberate act”, but police said there is no evidence to suggest there is a link with terrorism.

A second man, aged 24 and unknown to police, was arrested in close proximity to the scene after it was discovered he had a bag containing knives after he was seen filming the incident.

Police said the driver resisted arrested and that both he and the off duty police officer are in hospital.

Patton told a press conference on Thursday: “The actions of the off duty police officer, a sergeant, you would describe as heroic.

“To step in like that to an incident where you have seen such trauma at a hive of activity, not understanding what the threat is, to step in and take action and take someone into your custody, not knowing what he is risking himself, it’s heroic.”

Patton refused to reveal where the police officer works.

The incident left 19 people injured, four of whom are in a critical condition.

The driver arrested is an Australian citizen of Afghan descent with a history of drug use and mental health problems, police said. He was known to the police.

“He has been taken to hospital as a result of his injuries, as has the police officer,” Patton said.

“We don’t at this time have any evidence or any intelligence to indicate that there is a connection with terrorism.”

Victorian Premier Daniel Andrews called the attack on Flinders Street an “act of evil and an act of cowardice”.

One of the victims is a pre-school child who suffered a head injury. The child is not in a critical condition.

A witness told the Australian Broadcasting Corporation (ABC) that the vehicle was travelling at about 50 or 60mph.

“There was no breaking or any slowing down at all,” said Jim Stoupas, who said he was standing outside his donut shop when the car crashed into the people, one after another.

“All you could hear was just ‘bang bang bang bang bang’,” he said.

One witness said of the driver: “The only thing slowing him down was him hitting pedestrians.”

The incident began at 4.30pm local time (5.30am GMT).

All vehicle and pedestrian traffic has been advised to avoid the area on the city’s busy Flinders Street.

Major streets in Australian cities have been packed with holiday shoppers this week.

Flinders Street is a major road that runs alongside the Yarra River, in the central business district of Australia’s second-biggest city.

Police said there will be hundreds more police on the streets, but assured the public there is “no increased threat” to upcoming events.