Police and paramedics have been rushed to a major incident with "number of casualties" reported.
Up to 30 emergency vehicles were sent to Baglan Street near Treorchy, where police cars have been parked up and an air ambulance was dispatched.
South Wales Police said the street has been closed off and people are advised to avoid the area until further notice.
A force spokesperson said: "Police units are currently dealing with a serious incident which occurred in Baglan Street, Treorchy, at approximately midday today (5 March, 2021).
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"Ambulance crews are also in attendance as the incident involves a number of casualties.
"The street has been closed off and people are advised to avoid the area until further notice. Anybody who may have witnessed the incident is urged to contact 101 immediately and give reference *077519."
A spokesman for the Welsh Ambulance Service said they had sent one rapid response vehicle, three emergency ambulances, the hazardous area response team and the Wales Air Ambulance to the scene.
Chris Bryant, Labour MP for Rhondda, tweeted that he is aware of “disturbing events on Baglan Street” and said his thoughts go out to all those affected.
A resident told Wales Online: "I live in the street, it was about half past 12 on my way to meet my friend.
"They were saying can you get back. Then a couple of minutes later I saw someone getting stretchered off into the back of an ambulance literally outside the Chinese by the hill."
One neighbour said she saw “quite a few police cars” arrive in the area and knew it must be “something serious”.
Mavis Wakeford, 79, told the PA news agency: “It’s quiet, nothing like this has ever happened. I’ve lived here all my life and nothing like this has ever happened before.”
She added: “It’s something serious, obviously, it’s got to be, hasn’t it?”
Councillor Andrew Morgan, the leader of Rhondda Cynon Taf County Borough Council, said he had been informed of “the major incident in Ynyswen” and thanked the emergency services for the “significant attendance which is ongoing”.
He added: “My thoughts are with everyone affected by this incident but please avoid the area until emergency services leave the location.”
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