There are over 30 documented shipwrecks on Rhossili Beach

Surfers raised the alarm about the obstacles at Llangennith on Gower, which although visible at low tide are hidden under water as the sea comes in.

Initially it was thought they may be the top of a ship but wreck expert Jim Phillips has now ruled that out.

He believes they are railtracks sunk into concrete, buried below the sand.

There are warnings of a serious injury if someone were to hit one of them.

After visiting the site at low tide on Wednesday, Mr Phillips said they were likely to date back 65 years.

Mr Phillips, who has researched many shipwrecks around the Swansea and Gower coast, said many such constructions were placed on the beach during World War Two.

They will have to be removed Jim Phillips

He said they were used both as obstacles for invading forces and for British servicemen to practice with explosives.

"The surf has moved the sand which has exposed them," he said.

Mr Phillips said they were covered in dead plant and shell life which suggested they had been exposed before.

"The sand could shift again and cover them tomorrow or they may stay exposed for a long time to come.

"They will have to be removed - they are a danger if you don't know they are there," he added.

He said at low tide they were protruding about 18ins (45cm), and were about 25m (82ft) apart.

They are more or less opposite the main footpath from the car park.

Richard Dallimore of Llangennith Surf said they could cause someone a serious injury if they were to collide with one of them on what is Gower's most popular beach for surfing.

"The sand has been shifted quite a lot by the winter swell we've had this year," he said.

"The posts are in the busiest area where everyone ends up.