Update - 1.16pm: An 18-year-old man has been arrested on suspicion of causing injury by dangerous driving after a car ploughed into crowds in Newport.
A spokeswoman for Gwent Police said: "Following the incident this morning on Cambrian Road in Newport involving a car and four pedestrians, an 18-year-old man from the Newport area has been arrested on suspicion of causing injury by dangerous driving.
"Investigations are ongoing and we'd like to thank everyone for their comments and shares."
11.10am: Four injured after car hits pedestrians in Wales
Four people have been taken to hospital after being struck by a vehicle in Wales, police said.
Emergency services were called to Cambrian Road in Newport, south Wales, at 5.30am on Sunday to reports of an incident involving a vehicle and pedestrians.
Gwent Police said it is believed that a blue Ford C-Max collided with four people - three women and a man.
Following the incident, the driver - described as black and aged in his twenties - made off in the direction of Maindee.
The vehicle was later found burnt out on Magor Street in Newport, a force spokesman said.
"All of those injured have been taken to hospital for treatment," he said.
"Their conditions are currently being assessed but it's believed that two of the girls have received potentially life-changing injuries."
Cambrian Road is closed while investigations continue.
Superintendent Glyn Fernquest said: "This is a shocking incident for everyone involved.
"Specialist officers are currently investigating and are appealing for information in relation to identifying the driver of this vehicle.
"I'd like to just reassure the public that this incident is not believed to be terror-related and has no links to the Newport marathon that is taking place this morning.
"Anyone who is taking part in the marathon should carry on with their arrangements as planned."