A fire at the former Crumlin Road courthouse in Belfast is being treated as deliberate.
The fire broke out at around 2.40am on Monday with four appliances sent to the scene with 25 firefighters working to bring the blaze under control.
Crews remained at the scene on Monday morning with the Fire Service saying it was believed to have been a deliberate ignition.
It's thought the fire broke out in one of the courtrooms.
Police said they too were treating it as deliberate and have launched an investigation.
Sinn Fein MP John Finucane praised the actions of the Fire Service.
"The old Crumlin Road courthouse building is one of the most historic and recognisable in the city and this deliberate attack on it is wrong and must be condemned," he said.
"Thankfully no one was hurt in the incident and I want to commend the actions of the firefighters involved in bringing the blaze under control.
"There are ambitious plans for the regeneration of the site which will provide a boost to the local economy and those will not be helped by this."
Belfast councillor Alderman Brian Kingston described the latest fire as "tragic" and praised the work of the Fire Service in preventing its spread to nearby homes. He said it was "deeply frustrating" none of the plans for the site's redevelopment had come to fruition.
“There are reports locally of young people having been on the site over this past weekend, whether or not that is connected to the fire. I would appeal for anyone with relevant information to pass that on to the PSNI," he said.
“It would be a tragedy if this fine listed building were to be lost. There is the need now for renewed statutory sector involvement in determining its future direction.
"It cannot just be left in the hands of private developers while it continues to deteriorate and to be damaged. In the immediate term, we will be making urgent representation for the premises and the site to be secured while an assessment of its condition takes place.”
The iconic courthouse - once an architectural treasure - sits derelict opposite the refurbished Crumlin Road Gaol in the north of the city.
The 19th century building designed by Sir Charles Lanyon, which was the venue for the most famous - and infamous - cases of the Troubles closed in June 1998.
There have been numerous fires over the past two decades with the most devastating in 2009.
Plans for a hotel development have so far not moved beyond the preliminary paperwork stages.
In 2018 the council gave planning permission for a £10million 77-bedroom hotel to the Liverpool-based Signature Living Group.
The group has run into problems with plans to open the George Best Hotel in the centre of Belfast which went into administration at the end of April.
Initially the company planned to open the courthouse hotel in the summer of 2019. It has since been placed for sale by the group.
The Crumlin Road Courthouse, designed by Sir Charles Lanyon in the 1840s, has been an important part of the city’s story for generations.Belfast Buildings Trust
The council in September last year expressed concern at the lack of development on the site particularly given its inclusion in the development of the city's tourism strategy.
The Belfast Buildings Trust (BBT) expressed its sadness at the fire.
Shane Quinn, development Manager of BBT, added: “It is hugely troubling to see yet another fire cause yet more damage to the building, and especially to hear that it has been started deliberately.
"We thank NI Fire and Rescue Service for their quick actions.
"The courthouse’s physical history and the personal stories associated with it say so much about Belfast.
"BBT has worked with various agencies and owners over the years. We obviously need to wait and assess the full extent of the damage, but we remain convinced that a suitable use can regenerate the building and be a catalyst for wider regeneration in north Belfast.
"Unfortunately, we’ve grown all too used to historic buildings in the city being destroyed by fire.
"But, as we saw after the [Primark] Bank Buildings fire, historic buildings are often at the very heart of our city’s lives and hold huge meaning for people.
"We all have to recognise that heritage buildings aren’t about the past. Everyone in Belfast now has a responsibility to make sure that we double our efforts to find a long-term use for the Crumlin Road Courthouse. No building is beyond saving.
"The Trust believes that whilst last night’s fire is devastating for the city to wake up to, with determination and the involvement of local people, we can make sure heritage is at the heart of our city’s regeneration.”
Assistant Chief Fire & Rescue Officer Paddy Gallagher said the fire service had to deal with the courthouse incident just hours after battling a major grass fire at Gullivers Avenue.
"Thankfully no one was hurt and due to the quick actions of our Firefighters the fire did not spread to any other properties," he said.
“This was a significant fire that came at the end of an extremely busy weekend for Northern Ireland Fire & Rescue Service and I want to thank all of our Firefighters who have stepped up to the mark over the last couple of days, as well as all of our partner agencies who have worked closely with us in responding to a number of challenging incidents.”
A PSNI spokesman added: "Police in north Belfast are investigating a fire at Crumlin Road Courthouse in the early hours of Monday June 1.
"A report was received at around 2.55am on Monday morning of a fire at the building. NIFRS attended and extinguished the fire which is being treated as deliberate at this time.
"Officers would ask anyone with information which could assist them with their enquiries to contact police at Tennent Street on 101 quoting reference number 213 01/06/20.
"Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime. You can also make a report using our online non-emergency reporting form via http://www.psni.police.uk/makeareport/."
Signature Living has been approached for comment.