UPDATE 3.30pm:

The fire service is now scaling back the response to the fire. 

East Sussex Fire and Fescue Service said: 

"There are now five fire appliances on the scene. Kingsway road has been cleared of fire debris to enable Sussex Police to lift local road closures.

Whilst the smoke at the scene has significantly diminished, the advice is still to keep windows and doors closed.

A joint investigation between Sussex Police and East Sussex Fire & Rescue Service has begun to determine the cause of the fire."

The Argus:

Update 2pm

The fire is still burning. 

There are currently ten fire engines in attanedance still trying to damp down the flames. 

The exact cause of the fire is still unclear. 

East Sussex Fire and Rescue Service said: "Efforts are being made to surround the fire."

Latest update 11:50am

Neighbouring residents have been urged to keep their windows closed. 

Eyewitnesses have reported that the fire is believed to have been started by a disc grinder sparking. 

Witness Emma Chic was one of the first on the scene and took the picture above.

She said: "I was out for run and to start with just thought it was massive grey cloud. 

"I kept running towards it. 

"I dont have any sense of smell so it was only when I got up close I realised how bad it was." 

The Argus: A major fire erupted in Portslade this morning at about 8.50am.

Large plumes of dark smoke are billowing into the sky and emergency services are at the scene.

In their latest update East Sussex Fire and Rescue Service said: "Crews are responding to a serious fire in Portslade at Chandler Building Supply’s, Basin Road, North Portslade. There are now eight fire appliances in attendance at the scene along with two aerial ladder platforms and a water bowser.

"The fire is in a store room of the builders merchants and the building is well alight. The building is approx 13m x 25m. Crews are currently tackling the fire.  

"Due to large volumes of smoke in the Portslade, boundary area, the public are advised to avoid the area. Sussex Police have also implemented road closures in the area and traffic is busy.

"Six fire appliances responded initially from Hove, Shoreham, Roedean and Newhaven along with a further two from Preston Circus.

"A further two fire appliances have now been dispatched from Lewes and Newhaven along with two aerial ladder platforms from Preston Circus and Worthing along with a water carrier."

No one is thought to have been injured. 

Buses are being diverted from Kings Road  along Church Road. 

Police are currently on the scene. 

A spokeswoman for Chandlers Building Supplies said: "Firefighters are currently at the Brighton branch of builders merchants, Chandlers Builders Supplies located at Basin Road North, Aldrington Basin, Portslade. The Chandlers Building Supplies Brighton branch will be closed today.

"The fire service is working at getting the situation under control. It appears that the fire started early this morning.

"We do not know any further details at this stage. Most importantly, nobody has been harmed or injured."

There are three warehouses at the site. One is understood to have collapsed. 

Residents have been sharing pictures on social media.

More updates will be available soon