A huge fire that closed Nottingham railway station is being treated as arson.
At its peak 10 fire crews were tackling the fire, which began at about 06:30 GMT.
Flames were seen coming from the station's roof and smoke filled the foyer, prompting the building's evacuation.
Supt Sandra England said: "We now have reason to believe the fire may have been started deliberately."
She added: "Cordons remain in place around the area and trains are not running. It is likely the station will remain closed for the rest of the day."
Incident commander Bryn Coleman, from Nottinghamshire Fire and Rescue, said crews faced "arduous" conditions when they arrived to tackle the "severe" fire that spread across the concourse.
He described the operation as "difficult and protracted".
He added the fire was believed to have started in a toilet.
The fire service confirmed in the early afternoon that a joint investigation with the British Transport Police was already under way.
At 17:00 GMT crews were still at the scene dealing with the fire, which has been brought under control.
British Transport Police said it was an "ongoing incident" and said the station was "unlikely" to be open by Saturday.
Supt Sandra England said: "Even if some trains are running by tomorrow, there will be an extremely limited service with many delays, cancellations and overcrowding."
She advised football fans travelling to and from Nottingham for matches on Saturday not to attempt to travel by train.
East Midlands Trains said while no-one was injured and everyone was accounted for, all services, including trains to London St Pancras, Liverpool, Leicester and Norwich, have been disrupted.
There will be no trains to and from Nottingham for the remainder of today as soon as we have an update withto tomorrows situation we will post here: https://t.co/HGrKnOxIEZ gard ^AL— East Midlands Trains (@EMTrains) January 12, 2018
Kirsty Derry, deputy managing director of Stagecoach, East Midland Train's parent company, apologised for the disruption but said they were "really optimistic" about services at the station on Saturday but warned there would be "gaps".
About 4,600 passengers arrive at Nottingham station during each weekday morning between 07:00 and 10:00, according to the Department for Transport.
The station has recently undergone a £50m redevelopment, incorporating a new tram bridge, including the restoration and upgrade of its Edwardian grade II listed front building.
Eyewitness Sarah McMullan said she saw smoke coming from a toilet at the station's car park.
"You don't think much of it when there's a little bit of smoke and police already there, but then we were evacuated," she said.
"It was pretty frightening to see how quickly a fire can grow. You can see billowing smoke and flames above the roof on the far side."
BBC Radio Nottingham's Andy Whittaker said he saw "thick plumes of black smoke" coming from the station.
He said many people were left waiting outside the building after being told to leave.
Dr Remigius Ilione, 49, said: "I drove into the car park and I could already hear the fire alarm.
"The smoke was so thick that you could not see in front of you."
Queens Road and Carrington Street were closed in both directions, which created heavy traffic on surrounding routes, but while there have been partial reopenings, disruption remains.
There have been reports of 40-minute delays on bus services.
Trams into the city were also disrupted by the fire and a separate incident, but began to run past the station at about 14:30 BST.
Visiting the station, Transport Minister Jo Johnson said: "It has been a devastating incident, but it has been an extraordinary response from the emergency services.
"We saw an exemplary evacuation this morning. There were about 200 or 300 passengers at the start of the rush hour who were evacuated safely.
"As far as we can tell no-one has been hurt in the incident and we really do owe a huge debt of gratitude to the emergency services. East Midlands Trains has done a great job ensuring no-one was hurt and everyone was evacuated safely. "
He added that he hoped the station should be back up and running in the "next few days".