An Irish person is among 19 people injured after a car was driven into crowds in Melbourne, Australia.
The Department of Foreign Affairs has said it is aware of the case and is providing consular assistance.
The driver arrested following the incident was a 32-year-old Australian of Afghan descent with a history of drug use and mental health problems.
Victoria Police chief Shane Patton said a second man, aged 24, who was arrested after he was seen filming the incident was found to have a bag containing knives.
Investigators have found no evidence to suggest a link with terrorism and Mr Patton said they had not established any relationship between the two men.
Some 19 people were injured, four critically, when a white car was driven "in a deliberate" act at crowds outside Flinders Street station at around 4.30pm local time.
Witnesses described "people flying everywhere".
Video: Emergency services respond as car hits crowds in Melbourne pic.twitter.com/5VuK7Sf6fC
— RTÉ News (@rtenews) December 21, 2017
Images from the scene showed a number of people receiving medical attention, while a white Suzuki SUV appeared to have crashed to a stop.
The driver of the car was detained by an off-duty police officer, who was later taken to hospital with injuries not believed to be critical.
Mr Patton told the press conference the driver had resisted arrest.
He added: "We have reviewed the footage and are satisfied that he was driving the car without anyone else present.
"He has been taken to hospital as a result of the incident, as has the police officer.
"He is a person known to Victoria Police. He has historical assault matters and has a history of drug use as well as mental health issues.
"We understand that he was on a mental health plan and receiving treatment.
"We do not at this time have any intelligence to indicate that there is a connection to terrorism."
Paramedics have now transported 13 people to city hospitals. Two more people are being assessed by paramedics at the scene.
— Ambulance Victoria (@AmbulanceVic) December 21, 2017
Police said they had "saturated" the area with officers as paramedics transported 13 people to city hospitals, while two people were being assessed by paramedics at the scene.
One witness told 3AW radio: "As it (the car) approached this intersection ... it just mowed everybody down, people were flying everywhere."
Police are currently attending an incident on Flinders Street between Elizabeth and Swanston streets where a vehicle has collided with a number of pedestrians. Police have arrested the driver of the car. Extent of injuries are not known at this stage. (1/2)
— Victoria Police (@VictoriaPolice) December 21, 2017
It was the first week of school summer holidays in Victoria, and the area was busy with Christmas shoppers.
"The driver of the vehicle and a second man have been arrested and are in police custody," police said.
"A number of people were treated at the scene for a range of injuries and have been transported to hospital.
"A crime scene has been established and all vehicular and pedestrian traffic are advised to avoid the area."
Australian Prime Minister Malcolm Turnbull tweeted: "As our federal and state police and security agencies work together to ... investigate this shocking incident, our thoughts and prayers are with the victims and the emergency and health workers who are treating them."
Kyra Gillespie was one of "hundreds of people" who were told to get off trams near the area following the incident.
She told ABC News: "I think everyone is a little bit shaken up by the experience.
"Lots of people were phoning their loved ones to tell them they were okay."
In January, four people were killed and more than 20 injured when a man deliberately drove into pedestrians at a spot just a few hundred metres away from Flinders Street incident.
Police said the January incident was not terrorism-related.
