Emergency services are responding to reports of a serious assault in Aberfan, South Wales Police have said.
Armed officers are in the area, police said, and residents have been urged to avoid the area.
The incident took place on Moy Road just before 9.10am this morning. Paramedics say a person has been taken to hospital.
A school and a childcare centre have been placed in lockdown while police deal with the incident.
Trinity Childcare and Family Centre said: “We are currently in lockdown as a precaution due to an incident within the community. All staff and children are safe.”
Rhiannon Stephens Davies, head teacher of Greenfield School, said: “We are aware of an ongoing police incident in Aberfan.
“We just wanted to reassure you that as a precaution we are keeping the pupils safe inside the building, and all perimeter gates are locked.”
A Welsh Ambulance Service spokesperson said: “We were called today at approximately 9.10am to reports of an incident in Aberfan, Merthyr Tydfil.
“We sent one emergency ambulance, one air ambulance and one Cymru High Acuity Response unit to the scene where advanced critical care support was delivered.
“We conveyed one patient by road to the University Hospital of Wales, Cardiff for further treatment.”
Gerald Jones, MP for Merthyr Tydfil and Rhymney, said: “I have spoken to police regarding a serious incident in Aberfan this morning.
“You may see an increased police presence in the area, and I’d encourage everyone to co-operate with police officers as they deal with the incident.”
Welsh Senedd member, Dawn Bowden, said: “I am aware of a serious incident in Aberfan this morning.
“I have spoken to the police and will await further information from them.
“However, please take advice given by the police, who will be grateful for your co-operation while this incident is dealt with.”