Police investigating an attack on a five-month-old baby boy on a Tyneside Metro station platform have arrested four people.
The child is said to be "gravely ill" in hospital.
He suffered severe facial injuries in the assault at Manors station on the outskirts of Newcastle city centre on Sunday afternoon.
Despite the arrests, detectives investigating the incident still need help from the public to establish exactly what happened to the baby.
Officers found the injured child in a blue pram on the platform.
A Northumbria Police spokesman said: "The baby, who is not being identified, was with an adult in the station.
"For reasons which have yet to be fully established the baby has suffered head injuries believed to have taken place on the platform.
"Exactly what happened in the Metro station is still being investigated.
"The baby boy was taken to Newcastle General Hospital where he is now said to be gravely ill.
"Police urgently need to speak to anyone who was in the station or on board a train that may have seen an incident involving a group of youths or an adult with a pram.
"Four people have been arrested in connection with this incident but we still need help from the public to assist the inquiry."
The police appeal included a tape-recorded broadcast being played across the Metro network urging anyone with any information to contact police.
Officers closed Manors station after launching an investigation.
Metal shutters were up at the building this morning, with a policewoman posted outside the main entrance.
A handful of commuters turned up, unaware that it was closed.
The stop is on the edge of the city centre and close to the central motorway.
One worker arriving at a nearby business park, who did not want to be named, said: "It is shocking that this can happen. But it's surprising, because the Metro system is usually well staffed."