A 13-year-old girl has been stabbed and six teenagers arrested on suspicion of attempted murder.
Humberside Police said she was found at the side of the A63 dual carriageway in Hessle at about 07:00 GMT.
She suffered "lacerations" to her neck, chest and abdomen and her injuries are "life-threatening", the force said.
Four boys aged 14, 15, 16 and 17, and two girls aged 14 and 15 were arrested soon after in a wooded area nearby.
Det Supt Simon Vickers said he believed the attackers knew the victim, who is in a critical condition in hospital.
“I understand this incident will rightly cause concerns amongst the community and I would like to offer my assurances that as a part of our initial investigation we have six individuals in custody who are all being questioned by detectives," he said.
“At this time, we do believe the attackers knew the victim and inquiries are ongoing to establish the circumstances around the incident."
Det Supt Vickers thanked those who helped the seriously injured teenager on the side of the road before emergency services arrived.
Searches took place in an area near the Hull Humber View Hotel in North Ferriby, near Hessle.
The force has appealed for anyone with information, particularly those who have dashcam or CCTV footage, to contact police.
A cordon has been put up around the wooded area off Ferriby High Road.
As darkness fell in North Ferriby, about 12 police officers continued to search land close to the A63 until about 18:00 GMT. It's an area criss-crossed by busy roads, where there are pockets of woodland.
The search was in a field between the railway line and the dual carriageway but it extended into the surrounding woodland.
Officers ducked in and out of a nearby hotel - the Hull Humber View Hotel appearing to be a temporary base for those involved in the investigation, which has been active since reports emerged of the stabbing nearly 12 hours ago.
