Some of the tractors had signs attached reading "no farmers, no food" as the agricultural workers sought to remind people of their important role in day-to-day life.

Motorists could be heard beeping their horns while sirens could also be heard as police cars moved slowly through the traffic.

Videos shared with Sky News from a passenger in a car travelling in the opposite direction showed at least 88 tractors were involved in the action on Friday.

Dyfed-Powys Police posted at around midday on Friday that it expected the disruption on the A48 to last "another few hours".

"Traffic is moving very slowly... We believe they intend to travel to Pont Abraham, before heading back towards Carmarthen along the westbound carriageway."

The force urged those who were planning to travel between Carmarthen and Pont Abraham on the A48 to consider choosing another route.

The latest demonstration comes as farming unions have expressed their concern about Welsh government proposals which could mean the current basic payment scheme is replaced by the sustainable farming scheme (SFS).

This would become the primary source of government funding for farmers in Wales.

Farms would be rewarded for actions that meet specific climate obligations.

One of those conditions would be for 10% of farmland to be covered with trees by 2030.

While this applies only to land where conditions allow, farming unions are worried about the long-term future of the industry with those additional regulations.

On Tuesday, a man was charged after a farmers' protest involved a number of tractors being parked outside the office of the Welsh government's rural affairs minister, Lesley Griffiths.

Last week, around 3,000 farmers gathered in a livestock mart in Carmarthen, West Wales, to oppose the Welsh government plans.

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The Welsh government says the sustainable farming scheme aims to "keep farmers farming" and "safeguard the environment".

"The final consultation on the scheme is still open and we encourage everyone to reply with their views by 7 March," a spokesperson said.

"No final decision will be taken on the scheme until after the consultation has taken place, and we will listen carefully to all views."

The famers' protests in Wales come after recent demonstrations by farmers in France, and in many European countries, who are opposed to their governments' regulations and are concerned about a fall in income amid rising costs.