A major search operation was launched overnight after a teenage boy went missing while playing in a river.
Witnesses have described seeing a helicopter and police with torches in Lechlade-on-Thames, Gloucestershire, in the early hours.
A police spokesman has confirmed to the Mirror the incident is ongoing - with emergency calls made around 10pm on Sunday.
Those involved are estimated to be all aged around 17 and are believed to have been camping near The Round House, a former lock-keeper's post and now a listed building.
There is some suggestion the group may have been jumping into the water from a wooden footbridge.
It is understood four teens were pulled from the water and treated near The Riverside pub last night.
They were also seen in the back of an ambulance wrapped in metallic blankets.
Search boats looking for the missing boy were launched from Lechlade Marina.
Police this morning were briefing about the flow of the river and where to look next - with numerous local independent rescue groups involved.
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A boater, who moored up near the pub last night, said he offered to take initial emergency crews upstream soon after they arrived.
The 66-year-old told the Mirror: "I was on board last night and saw when the search and rescue helicopter came about 10.45.
"Ambulances and rescue people from Filton arrived and asked me whether I knew the river. I said yeah, I know it well. They asked me to describe it and how far up this bridge is where they were jumping off from and camping.
"I got out a map and showed them. I said if you want to go up the river...boat’s warmed up, engine’s going, you can stand on the front with a torch, I’ll give you a light and we’ll go upstream and have an initial look.
"It was the golden hour of trying to get someone out the water when it’s this cold.
"He said he’d bare that in mind, then he came back and asked us how to go down to St John’s lock, which is the first lock on the Thames."
He said the search parties assembled outside the pub.
"The landlord was very good and offered facilities, re-opening up the pub," he continued.
"I was just on the side, on the mooring, keeping myself to myself, but offering advice when it was asked for."
He went on to say: "They were camping half a mile upstream near the Round House - there's a wooden bridge across the river.
"Some people say they were jumping in from there, others say two of them slipped in and it wasn’t jumpers.
"It could have been they slipped in off the riverbank."
Asked what the scene was like this morning, he said: "It is very active today. They’ve got lots of local search and rescue operators from around the county because we’re on the border of Gloucestershire, Oxfordshire and Wiltshire.
"It’s a fair bit of water...We’ve got several rescue vessels and incident control here."
A Gloucestershire Police spokesperson said: "Searches have been taking place in the River Thames after a report a teenager was in the water near Lechlade on Thames.
"Police were called at around 10pm yesterday (Sunday 30 April) and emergency services attended.
"Officers have been supported by the National Police Air Service, Gloucestershire Fire and Rescue Service and Severn Area Rescue Association while searches continued into the early hours of this morning (Monday).
"The teenage boy has not yet been located, and specialist search teams will be continuing with the search today (Monday). His next of kin are aware.
"A group of four had been at the location together, and some had entered the water to try and find the boy. They are all accounted for."
A spokesman from Gloucestershire Fire and Rescue Service said: “We were called at 10.03pm by the coast guard to reports that some teenagers believed to be aged about 17, had been playing in the river at Lechlade and one hadn’t resurfaced.
"We assisted the search by sending three crews from Fairford, Gloucester South and Tewkesbury, along with boat crews.
"We liaised with coast guard and the police, who were co-ordinating the search, and came away from the scene at about 4am.”
A spokesman for Severn Area Rescue Association (SARA) said: "We were called by Gloucestershire Police last night to assist fire services after an individual had been reported to have gone into the river."
He added that one of the organisation's boats was taken down to the scene.
A team has also been deployed from Wiltshire Search & Rescue.
