Four people have been taken to hospital after being struck by a vehicle, 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."
Anyone with information should call 101 quoting log 110 29/4/18