People have been advised to keep their windows and doors shut due to a widespread fuel leak in the River Taff.
Kerosene has spread down almost 2.5 miles (4km) of the river, Natural Resources Wales (NRW), has said.
It was first reported to be affecting at least one mile (1.6km) of the river on Saturday morning, then NRW later said it had spread as it continued “to investigate the source of the incident to understand how it is happening, stop the pollution completely and collect evidence”.
Eurig Thomas, a resident in Taff’s Well, Rhondda Cyon Taff, said: “It smelt like a petrol station, it hit you as soon as you came out.”
Absorbent materials have been deployed to try and contain the leak.
Thomas added: “The river had a shiny sheen on it, the stream flows behind my house, it comes down from the GE factory and into the Taff.
“The smell has dissipated – but you can still smell it this morning.”
Another resident, Sarah Llewelyn, added: “I haven’t slept in three days. Friday afternoon lunchtime I opened the door and could smell fumes, it was burning my eyes.”
She said South Wales Fire and Rescue went to the GE site on Friday, stopping the flow, and dubbed it “a national disaster”.
“NRW have told us that up to 25,000 litres of kerosene has entered the river.”
Gareth Llewelyn, a former hazardous materials environmental protection officer with South Wales Fire and Rescue service, said there was “no quick fix” and it needed “years not months” to restore.
He added: “I have visited the culvert across the road from the GE site yesterday and it was full of kerosene. It doesn’t mix with water and will continue to pollute.
“They’ve torn the heart out of our community, the village is Taff’s Well – it’s named after the river.
“They’ve literally killed our river, if you go down there now there’s no animals, no birds, they’ve killed all the fish.”