Emergency services including rescue boats were scrambled to a bridge in Carmarthen to a man apparently in distress.
The incident happened on the A40 between the Abergwili and Llangunnor areas of the town.
Police were called to the scene following "concerns for the welfare of an individual" on Pont Cynnwr, a bridge that forms part of what is known locally as Carmarthen bypass. Fire and rescue reams were also in attendance, and an eye-witness said “police were everywhere”.
One motorist who was driving past the scene on Sunday lunchtime described how officers were talking to a man who was “stood leaning over the barrier”.
The incident led to police closing the dual carriageway that runs alongside Carmarthen town centre in both directions for more than three hours.
This caused huge congestion which was described as “chaos” by motorists who were caught up in traffic being diverted through the town.
A spokeswoman for Mid and West Wales Fire and Rescue Service said: “We were called at 12.24pm on Sunday to assist police with an incident near the retail park in Carmarthen.
“We sent boat crews from Carmarthen and Swansea to the scene and a fire appliance from Carmarthen.
“We left the scene shortly after 3.30pm.”
A spokeswoman for Dyfed-Powys Police said: "We were called just after midday on Sunday, August 4, to concerns for the welfare of an individual on Pont Cynnwr, Carmarthen.
"Officers attended and for safety reasons the A40 dual carriageway between Abergwili and Llangunnor was closed from approximately midday to 3.30pm."
The condition of the man is not known but the police did confirm that he was taken to hospital following the incident.
Anyone seeking help can call Samaritans free on 116 123 or visit Samaritans.org
