Residents from 11 homes were evacuated, while the road remains blocked.
A Neath Port Talbot council spokesman said: "We are monitoring the situation on a daily basis."
Three flood warnings, at Monmouth, Tenby and in the Lower Dee Valley, remain in place.
In Ystalyfera at the weekend, landslips led to what council officials called a "dramatic movement" of soil and trees from the mountainside onto a road at Panteg near Ystalyfera in Neath Port Talbot on Saturday night.
Some trees came to rest against the vestry of a local chapel.
Banging on doorA house has been also left on the edge of a drop, where the land in front of it has slipped away.
A shipping container and a white transit van came to rest hanging over the road, held up by trees.
Pauline Jones was one of a dozen residents warned by the police to move out of their homes.
She said: "First of all we could hear the crackling of the wires coming down and then the police were banging on the door to say 'could you leave the property - is there anywhere you can go?'.
"And so we went over my daughter's and they kindly took us in the van. The street light was just blown to bits - all blue sparks coming from it."
Dramatic movement
Trees fallen against the vestry of Pantteg Chapel in Ystylafera after the landslip Council engineers inspected the damage on Monday with the owners of houses further down the slope worried because further rubble has been left overhanging the spot.
Some residents claimed the council should have done more to clear culverts and gutters and said they contacted the local authority only last week to warn that the land was becoming unstable.
Neath Port Talbot council's environment director John Flower said: "We were aware of an isolated small slip on the road which we were monitoring but what has occurred over the weekend are two slips at different locations along the road.
"The drainage is working. Our first concern is safety and we've closed the road and have identified 13 properties, two of which are empty and have taken the precaution of advising the residents for their own safety to vacate the properties. We are monitoring the situation on a daily basis."
A stretch of road about 200 yards (180m) long has been covered in mud up to four feet (1.2m) deep.
The council estimates the slip at "hundreds if not thousands" of tonnes of water-logged soil.
Mr Flower said: "Like many steep-sided valleys in Wales, there is continual movement but here we have seen some dramatic movement that has led to large deposits of material on the highway.
"It has brought down many trees. You can see trees at odd angles on the side on the mountain that are about to lose their roots."
Another landslip brought down a retaining wall at the back of a row of terraced home in Pontypridd, Rhondda Cynon Taf on Saturday night.
The 20ft wall collapsed in heavy rain, bringing earth and rubble onto the back gardens of homes in Berw Road. Four were evacuated.
The A4318 road was closed between Gumfreston and Tenby in Pembrokeshire Meanwhile, rail passengers heading from south Wales to London have been facing delays.
It follows flooding near Swindon, which means mainline services were being diverted and around 45 minutes were added to journey times.
On the roads, flood water is still creating problems for some drivers, in particular on the A48 at Bonvilston in the Vale of Glamorgan.
Emergency repairs have been carried out on some roads in the county due to flood damage, including on the road between Llantwit Major and Llyswerny and at the traffic light junction on the A4055 between Merrie Harrier and Barons Court in Penarth.
Routine maintenance manager Ken Evans said: "The Vale council's visible services department managed to source 10 tonnes of extra temporary tarmac from a local contractor to help with the emergency repair work."
'Extra care'By later afternoon on Christmas Eve there were still three flood warning in place in Wales.
BBC Wales meteorologist Derek Brockway warned of unsettled weather through Christmas week.
"There's more rain and heavy showers to come this week and given the ground is so wet and saturated there's an ongoing risk of further flooding," he said.
"It's becoming very windy on Friday with gales or severe gales developing, especially in coastal areas and high ground exposed to the southwest."
Environment Agency Wales is advising people to remain vigilant for potential localised flooding across many parts of Wales with the continued rain over the next few days.
A spokesperson warned that land is already saturated from recent heavy rainfall, and any further rain could quickly find its way into rivers and streams.
The spokesperson said that could cause localised flooding of roads and low-lying land from blocked drains, ditches and small streams.
