Four teenagers, believed to all be aged around 17, had been in the river near Lechlade-on-Thames when one of the boys went missing.

Some of the group had entered the water to try to find him, police said.

The National Police Air Service, Gloucestershire Fire and Rescue Service and Severn Area Rescue Association carried out searches into the early hours after police were called at around 10pm on Sunday.

Specialist teams launched a fresh search for him on Monday.

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 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.

"The teenage boy has not yet been located and specialist search teams will be continuing with the search today. 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.

"The others are accounted for."

A Gloucestershire Fire and Rescue spokesperson said: "We were called at 10.03pm by the coastguard 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 coastguards and the police who were coordinating the search and came away from the scene at about 4am."

The Dorset and Wiltshire Fire Service have been searching the area on Monday.

Severn Area Rescue Association teams at Sharpness, Tewkesbury and Upton-on-Severn have also joined the search.