Over 20 firefighters extinguished a large blaze in the Pennyburn area of Londonderry on Saturday afternoon after a large number of tyres were set alight.
The fire was at the site of the former Arntz Belting factory in the Pennyburn Industrial Estate on the Buncrana Road.
Smoke was seen billowing from the site of the fire out across the city.
The Northern Ireland Fire and Rescue Service and the PSNI both attended the scene.
NIFRS Assistant Group Commander for the Western area Brian Hetherington said it was believed that the fire was due to "deliberate ignition".
He said a couple of hundred tyres had been set alight on waste ground at the site.
Mr Hetherington said that four appliances attended the scene with 24 firefighters involved in extinguishing the blaze using foam.
Police said the cause of the fire "remained under investigation".
NIFRS crews arrived at the scene shortly before 4pm and the last crew left around 5.30pm.
Police closed the road at its junctions with the Springtown Road and Strand Road as firefighters battled the blaze.
Local residents were asked to stay in their homes and keep their doors and windows closed.
The Buncrana Road reopened after the blaze was brought under control.