Marc Malpas and Aaron Matthews died in the crash

The victims were named locally as driver Natalie Malpas, 20, her brother Marc, 16, and friends, brothers Aaron and Gavin Matthews, aged 16 and 19.

Their Renault Megane careered into a wall near Ammanford in Carmarthenshire at 2200 BST on Wednesday.

A Malpas family relative said the parents were too distraught to speak.

David Peck added: ""I have just arrived from London with my family to be with them and they are obviously in deep shock.

"You have to bear in mind that they have just lost two members of their family. It is a terrible loss.

Police said all four people were pronounced dead at the scene

"I'm not fully aware of what exactly happened but there is a police investigation under way at the moment trying to find that out."

Dyfed-Powys Police said they were looking at "all possible causes" for the crash on a straight section of the Pontamman Road.

Eyewitness reports say the car flipped over onto its roof and debris was scattered in neighbouring gardens.

All four, who had been playing pool at a local pub before the accident, were pronounced dead at the scene by paramedics. Marc's 15-year-old girlfriend Rachel Meed described how she had seen him just minutes before the crash.

After laying flowers at the scene, she said: "The last time I saw him he just said 'I love you and I'll see you later on'."

Rachel's mother Jeanette said: "He was a lovely boy - very thoughtful. He spent so much time with us over the last couple of months, I just expect to see him walking past our window."

The scene of the accident on the approach to Ammanford

She said that Marc's sister Natalie, who police confirmed was driving the car, has a young son.

The family are originally from Kent and had only recently moved to the area, while the Matthews brothers were originally from the Bridgend area.

David Harries, whose bungalow took the full force of the crash, said he had been watching the news when the crash happened.

"The next thing I knew, there was an enormous bang and all I could see outside was dust everywhere," he said.

"My first reaction was one of utter disbelief. This morning it's the same - I'm just shocked. We've been campaigning locally to get something done about this road for months and then something like this happens, confirming all our worst fears."

Mr Harries, 58, said he had only just finished compiling a petition about speeding on the road.

As spokesman for a local campaign, he typed a letter on Wednesday calling for urgent action.

He said there had been two accidents on the stretch of road in the last month and residents had written to police before.

Witnesses appeal

Insp Tom Edwards said that it was at the very early stages of investigation but they were "looking at all possible causes" and that speeding could not be ruled in or out.

"I can't confirm that speed was in any way a contributory factor in connection with this particular incident," he said.

He confirmed there had been four accidents that resulted in injuries on that stretch of road in the last five years.

They are anxious to trace the movement of all the youngsters leading up to the accident.

Carmarthenshire Councillor Lyn Llewellyn, who lives nearby, said the road was not known to be dangerous although there had been complaints over speeding.

He said: "It's difficult to imagine how this could have happened. There have been some incidents on this piece of roadway but I don't think there have been any fatalities."