Emergency services have spent most of the day dealing with a large fire at a tyre recycling plant in Port Talbot.
The blaze broke out near Docks Road in Aberafan just before 23:00 BST on Tuesday.
At its height, 21 appliances and 100 firefighters were needed to bring the blaze under control.
Crews spent most of Wednesday tackling the blaze, as well as damping down and cooling the tyres.
Nobody is reported to have been hurt, but nearby residents have been advised to keep their windows and doors closed.
Mid and West Wales fire service said it was making "excellent progress" in dealing with the fire but warned it may take some time as the incident involves deep-seated fires within a large quantity of waste tyres.
Cordons are in place and people have been advised to stay clear of the area.
Huwel Manley from Natural Resources Wales said he had been concerned about the site for "quite some time".
"We recently prosecuted the previous occupiers of the site in respect of this illegally stored waste and had already started the process of using our statutory powers to require its removal from the site," he added.
The fire also led to the closure of the A4241 Afan Way in both directions, which resulted in heavier traffic than usual on the A48 Talbot Road westbound.
The A4241 is expected to remain closed for some time.
"People may suffer some disruption to travel arrangements in and around the immediate vicinity of the incident, thus alternative routes should be followed where possible," the fire service said.
The smoke plume is being monitored by Natural Resources Wales and Public Health Wales, but there are currently no signs of any significant change in air quality.