A teenage boy is in a critical condition after being hit by a vehicle in an "incredibly tragic incident" in which a schoolboy was killed.
Emergency services were called to reports of two children being struck in Stock, Essex, at 08:20 GMT on Friday.
Police said the boy who died was aged 15 but have not yet released his name.
A man arrested at the scene in Stock Road on suspicion of causing death by dangerous driving has been released under investigation.
The 23-year-old was also questioned on suspicion of driving while unfit through drink or drugs.
He was further held on suspicion of causing serious injury by dangerous driving.
On Friday, Det Insp Mark Fraser said: "This is quite clearly an incredibly tragic incident which will be felt by many people across the area, not least the families of the two young victims.
"Our role is to establish the circumstances which led up to this incident, which we will do meticulously and I would ask people not to speculate, whether in person or online."
Mayflower High School in nearby Billericay, where both children were pupils, said it was "shocked and immensely saddened".
"We are supporting all of our children and staff today as we try to come to terms with this sad loss," said headteacher Damian Lee.
"We are a strong and close community and will ensure that everybody is given the necessary help."
Officers urged people with dashcam footage or additional information to contact them.