PART of the new Southern Distributor Road built over a rubbish tip has sunk into the ground.

The drop of two to three cm means a 100-metre strip of dual carriageway is being torn up for repairs.

The weight of the road on a stretch near the Big W store has pressed down on the piles of rubbish underneath - and there is no guarantee that the road will not sink further.

Contractors said the SDR would be ready at the end of June and then shifted the opening to the end of July, blaming the 'tidying up' of barriers and roundabouts.

Project manager Peter Frood said the problem was not behind the delayed opening of the road, which is now pencilled for "late August".

He said: "The embankment crosses an existing tip. There was always some settlement anticipated but it's greater than we thought. We are taking this opportunity to beef up the embankment."

Contractors will pull up the surfacing and fill the 100m stretch with reinforced concrete to raise the road level and spread the weight of the road.

The £55m SDR will link the M4 at Junction 24 to the Pont Ebbw roundabout to divert traffic away from Newport centre and boost access to business areas.

Mr Frood said there were localised patches of "deformation" where bits of the road had sunk.

He said the 'dip' caused a shudder for cars passing over it but was not a safety risk although the stretch has been closed to traffic while work takes place.

He added: "This is just extra work to do. It would be easier if this hadn't happened but we still wouldn't be finished until the end of August. That's still six months ahead of schedule."

He said the road could sink further once opened and added: "If it's a problem again it will deform very slowly over a couple of months and can be dealt with then."

The sinkage was first noticed around two months ago and repairs are expected to be finished in a week. Councillor David Atwell, shadow cabinet member for transport and a retired property developer, said: "When building on ground like this one expects problems with compaction. But the methods the contractors have used have obviously been ineffective.

"If they are having problems at this stage then heaven help us in six months' time. I am quite sure the council will not take possession until their engineers are happy."