Police have also cordoned off an area behind Pontypridd Railway Station - known as Taff Vale flats.
Forensic teams are present and entering the building - police officers are also present.
ITV Wales' hannah Thomas reports from the scene that police have now "sealed-off an area under the railway bridge in Pontypridd. We don't know whether it is connected to the ongoing incident in the Sardis Road area of the town."
In a statement on its website Pontypridd Rugby Club says there is no access to its site.
Supporters, partners and neighbours of Pontypridd RFC are advised that the Sardis Road stadium is currently not accessible.
This is due to a police investigation into a major incident in the vicinity.
The club will keep all concerned informed regarding access to the Sardis Road stadium as further information is received from the relevant authorities.
Watch Hannah Thomas's report from the scene of a major police operation in Pontypridd this evening.
Police have confirmed they are dealing with an incident in Pontypridd but are not issuing any further details at this stage.
There is a large police presence around the town's rugby club.
The police helicopter has also been deployed and a cordon is in place.
Police have told people in Pontypridd that the cordon around the rugby club could be in place until next week.Read the full story ›
Police officers are manning cordons around Pontypridd rugby club.
Police have been asked to comment.
Residents in Pontypridd say Maesycoed Road is closed due to an ongoing incident.
The police helicopter can also be seen hovering above the town.
Drivers are being urged to avoid Pontypridd town centre due to an ongoing police incident.
The council say there is traffic congestion in the area.
There are reports of a heavy police presence near Pontypridd rugby club.
Residents nearby say the police helicopter is circling above and there is police road block on Maesycoed road.