People have died following a serious crash involving a car and bus, the ambulance service has said.
Elwyn Street in Coedely, Rhondda Cynon Taf, is likely to remain closed through Tuesday morning following the crash around 19:00 GMT on Monday.
The Welsh Ambulance Service said it sent seven ambulances and three doctors.
A spokesman confirmed there had been fatalities, but could not give further details.
He added that the incident involved a bus and a car, and that they believed a motorbike was also involved.
Rhondda Cynon Taf council’s deputy mayor Dan Owen-Jones said he was one of the first at the scene, after receiving a call from someone living on the street.
In a Facebook post on a local community page, he said: “I have faced this evening tragedy and bereaved families at its worse, at times I was numb and helpless to the grieving families.
“I cannot even describe the pain, shock and suffering I have witnessed tonight… Horrific.”
Speaking to BBC Wales, he said: “It’s a distressing time for all. At this time of year it’s even worse.
“I was there immediately, about two minutes past seven. I had a call from one of the neighbours, it happened outside their home. I was on the frontline trying to do the best with the traffic control.
“Later on there was lots and lots of family and friends. It was very distressing to see the family, but understandable – if it was one of my family I would have wanted to be there.”
Local councillor Danny Grehan, who represents the Coedely area said the collision was a “terrible blow” for the area.
“From what I understand, local people were involved in the horrific accident, and this is going to hit the area very hard.
“Obviously from seeing people’s comments last night, a shockwave will go through the whole community.
“The pain is obviously going to be felt by the families of those who are part of this but also in the whole community and I would like to thank the Coedely community for opening the community centre last night for the emergency services that worked there.”
South Wales Police said the road would be closed “for some time” and drivers should find an alternative route.
Traffic was also building up on the A4119 which leads to the M4 at Miskin, the force added.
Stagecoach Wales has said that due to the road closure they were unable to serve Coedely.
“We will serve Tonyrefail and will be using the bypass to Royal Glamorgan. We apologise for any inconvenience caused.”
Alex Davies-Jones, Labour MP for Pontypridd, described the incident as “devastating news from our community”.
She thanked those who tried to help on Monday night on X, formerly known as Twitter, and added: “All my thoughts are with the families and loved ones affected by this.”