Workers were evacuated after fire broke out at a water treatment plant near Saltend this morning.
Firefighters were called to Yorkshire Water's waste water treatment works, in Hedon Road, after fire broke out at around 7.30am.
Motorists reported a huge plume of flames and then thick black smoke near the plant's new £3.5m odour control unit, installed recently to address concerns over smells from the plant.
A number of witnesses said they had heard an explosion.
One eye-witness said: "I was driving to work when I just saw all this billowing black smoke.
"The firemen are covering the flames with jets of water and it all looks under control now."
Staff at the treatment plant have been moved off the site and an investigation is under way into the cause of the fire.
According to Yorkshire Water, owners of the site, an odour control unit has been damaged.
Engineers will be seeking to access the site as soon as it is safe to do so in order to assess the damage and determine the likely impact for nearby residents.
Yorkshire Water has released a picture showing fire damage at the site.
Former Hull KR player Nick Pinkney, who now works for P&D Engineers in Tower House Lane, in Saltend, described seeing flames shoot out of a chimney.
He said: "It must have been 8am ish when I saw what looked like a giant firework. Flames were coming from the top of a chimney. It was spectacular.
"Then, the chimney toppled over. There was a lot of smoke, but the fire service seemed to deal with it pretty quickly."
Matt Thompson of Yorkshire Water said: "The fire has damaged the older, smaller odour control unit at the site.
"At this stage, we do not know the extent of the damage or what impact, if any, this will have on our ability to control odours from the site.
"The second larger £3.5m odour control unit is undamaged and working exactly as it should."
The site, which opened in 2000, processes 170 million litres of human and industrial waste a day.
A Humberside Fire and Rescue Service spokeswoman said: "The public is not in any danger. Obviously, people worry when they hear about an industrial incident.
"But the fire is out. We remain at the scene performing what we call cooling and monitoring - effectively, damping down.
"Officers will now be working to find out what caused the fire."
Humberside Fire and Rescue arrived on the scene at 7.38am and spent one hour fighting the fire which had broken out in one of the water filtration plants.
Four engines rushed to the plant after the initial 999 call and the blaze was finally put out just before 9am.
It is still not yet clear what caused the blaze and firefighters are remaining at the plant to monitor the scene of the explosion and for cooling purposes.
However, they say there is no risk to the public.
There are no reports of any casualties.
