People had to be evacuated from their homes following a large fire at an industrial unit.
Crews were called to the fire involving several vehicles near Pentrebach Road in Pontypridd at 19:00 BST.
Thick black smoke, which billowed into the air, could be seen for miles around and eyewitnesses reported hearing several explosions.
Residents have since been allowed to return home, but have been told to keep their windows shut.
Jennie Griffiths, head of control for South Wales and Mid and West Wales Fire and Rescue Services, said the fire involved a number of vehicles in the unit and a number of cylinders.
She tweeted that there was "significant structural damage to building".
Four fire engines and three water bowsers were sent to the scene.
Local resident John Paul Davies said: "The smell was stronger than rubber and I was covered in black soot.
"There was small holes on my t-shirt when ash fell on me. There was also quite a number of explosions going on."
And John Richards, who lives more than a mile away from the blaze, said thick black smoke could be seen right across the valley.
Police closed local roads as firefighters tackled the flames using specialist equipment.
The cause of the blaze is not yet known, but officers said no-one had been hurt.
A South Wales Police spokesman said: "A number of homes in Pentrebach Road and Graig-Y-Helfa Road were evacuated as a precaution.
"Residents can now return home but are advised to keep windows and doors shut."
Pentrebach Road remains closed to traffic.