About 100 firefighters are tackling a huge blaze at a building used for storing chemicals on the edge of a city centre.
People living in the centre of Leeds reported hearing a number of loud explosions as smoke and flames dominated the city's skyline for a number of hours.
Residents in the Albion Way area have been asked to keep their windows and doors closed as 15 fire crews from across West Yorkshire continue to fight the flames this morning.
A fire service spokesman said the blaze was now surrounded but it may take the rest of the day to extinguish the fire, especially as a collapsed building was making firefighting efforts technically difficult.
The fire at Tradpak Recycling spread to two other buildings but crews managed to save four other businesses on the industrial estate, officers said.
There are also reports the nearby Canal Mills arts and music venue was evacuated during the night.
Area manager Ian Dunkley, from West Yorkshire Fire & Rescue, told Sky News: "I t's been a really big job.
"We've had approximately 100 firefighters on scene - 15 firefighting appliances , two aerial platforms, a high volume pumps and various support appliances."
Mr Dunkley said: " When the initial crews arrived at just after two o'clock this morning, the fire was well developed and there was a series of large explosions where LPG cylinders were involved in the fire.
"Unfortunately two premises have succumbed to the fire but we've managed to save four surrounding companies and their premises, which is a really good effort by the firefighters in the initial stages.
"Our first couple of hours on scene was purely about saving surrounding premises."
Mr Dunkley said a fire investigation team was on site but it was too early to say what caused the blaze.
West Yorkshire Police spokesman said the force was called at about 2.34am.
The Armley Gyratory road - one of the main routes into Leeds city centre - was closed as a precaution due to the smoke.
The spokesman said: "Fifteen fire engines were deployed to the incident and cordons were established around nearby streets.
"Due to concerns about large amounts of smoke the Armley Gyratory Road was closed but has now re-opened. Roads remain closed around the site on the industrial estate itself.
"The matter is being treated as a large building fire by firefighters but, as with any fire producing large amounts of smoke, nearby residents are being urged to keep doors and windows closed while the smoke clears."
Soon after the fire broke out, local people took to social media to describe the scene.
Pat Hickey tweeted: " Got evacuated from canal mills. Leeds is on fire."
Anja Swan posted: " big explosions and what sounds like armagedon."
Firefighters said another firm involved in the incident was the packaging company Hazel Products.
A message on Hazel Products' website this morning said: " We greatly regret having to inform our customers that Hazel Products has suffered from a fire that started in the early hours of the morning on Monday 21 April 2014.
"Hazel Products is continuing to trade from a temporary location.
"Our dedicated team is working hard to prevent this event from adversely impacting our customers' operations and we will keep you updated."
West Yorkshire Police confirmed smoke from the fire was "not toxic" and said "swift work" by firefighters and police officers meant there was no need to evacuate any nearby homes or Armley Prison, which is about 300m from the scene.
Superintendent Mabs Hussain said: "We are continuing to assist our partners in the fire service in responding to what has been a major incident for Leeds.
"I want to reassure residents that everything has been done to get the fire under control and minimise the effect on residents.
"We can also confirm that the smoke from the fire is not toxic. However, as a precaution, we have continued to advise people near the site to keep doors and windows shut while the smoke has cleared, as we would do with any large fire."
He said: "The substantial operation at this site will continue for some time and police officers will begin to work with fire investigators to examine the cause of the blaze when the situation has been made safe.
"I wish to thank residents in the Armley area for their patience and understanding as emergency services have gone about their work, and also praise the efforts of colleagues in both services who have worked extremely hard to bring a dangerous situation under control."