Fire crews are still at the site of a blaze in the Duncrue Street area of north Belfast, after firefighters worked overnight to bring it under control.
The fire, which has been described as significant, broke out in a storage unit in the M2 Business Park shortly after 11pm on Thursday.
At its height, more than 60 firefighters battled to stop the blaze spreading to other properties.
On Friday, Northern Ireland Fire & Rescue Service confirmed that the fire in the agricultural feed store was accidental.
Four crews remain at the scene.
"The high rack shelving and roof in the premises have collapsed, and firefighters are working to extinguish the fire using breathing apparatus and a high volume pump," a spokesperson said.
“There will continue to be smoke in the area and we would advise the public to keep their windows closed and avoid the area if possible.
“It is expected that fire crews will be on site dealing with the incident into the afternoon."
The fire broke out at the distribution centre of agri-technology company Devenish.
In a statement, the company said: “Thankfully, no employees were inside the building during this time and the Northern Ireland Fire and Rescue Service were called to the scene quickly.
“This has not impacted production at our separate mill facility, which continues to operate as normal.
“We would like to thank the Northern Ireland Fire and Rescue Service for their incredible effort to tackle this fire throughout the night.”