The main train station at Glasgow Central will remain closed for the rest of this week following a huge fire that destroyed a neighbouring building.

Scotland's busiest railway station has been shut since Sunday, when a blaze spread from a vape shop on Union Street through a B-listed Victorian building.

Services from the smaller low level station, which runs services to Balloch and Milngavie in the west and Motherwell and Cumbernauld to the east, will resume on Wednesday.

But Network Rail said the high level station, which is used by the vast majority of routes, would stay shut for the rest of this week.

BBC Scotland News understands that Network Rail staff believe there has not been serious damage inside the station, and that its concourse is in good shape.

However, Network Rail said there was a "high level of instability" to the building façade on Gordon Street, which requires building assessment work.

Staff and fire service teams are continuing to work on the site and disruption to services is expected to continue for the coming days.

Network Rail route director Ross Moran said: "Unfortunately, further work is required to ensure the high level station is safe for trains to operate.

"We want to reassure passengers that we are doing everything we can to open the high level station, but we must enable the emergency services and Glasgow City Council to complete their critical work to secure the Union Corner site and make it safe."

Glasgow Central is one of the busiest stations in the UK, with 25 million passenger visits each year.

It is the main station for all services on the west coast mainline to England and also operates services throughout central Scotland.

A fire break between the Union Corner building - which was destroyed in the blaze - and the external wall of the station is thought to have stopped Sunday's inferno spreading further.

What needs to happen for Glasgow Central Station to reopen?

A step-by-step process will need to be undertaken before the main station can re-open.

Hot spots in the rubble must be damped down to prevent fire from flaring up again. Once the fire service is confident the fire has been extinguished, it will hand the site over to Glasgow City Council.

The local authority will then decide what happens to the remains of Union Corner. The façade of the building is still standing and could cause damage to the station if it fell.

It is thought that demolishing the façade would make reopening the front entrance of the station on Gordon Street much more straightforward.

After that, Network Rail will began carrying out safety inspections to determine when services can resume.

The belief at this stage is that the glass roof of the station does not appear to have suffered significant damage.

Made of metal, it is likely to have been heated when the blaze was raging, then cooled and doused with water as the fire was overcome, so it will need to be inspected for damage.

Controlling the flow of trains will be another key consideration, but the station does not appear to be central to this process, even if all its computer systems are not back online.

That is because the points system - which regulates the flow of trains in and out of the station - is controlled from another secure site elsewhere in Glasgow.

Electrical overhead lines were switched off when the fire took hold, which is standard procedure. They are also controlled from elsewhere on the network.

The tannoy system and announcements are controlled from within Central Station, but Network Rail may choose to live without this.

Network Rail Scotland's route director Ross Moran previously said when the fire service response moved into the "recovery stage", engineers would inspect affected areas of the station to assess what damage had been done.

Moran said the company was "extremely grateful" for the hard work of the firefighters.

About 250 of them worked around the clock to contain the fire in the Orr and Sons building on the Union Street junction with Gordon Street.

The building, known as Union Corner, dates back to 1851 - pre-dating the station which opened in 1879.

Speaking in the Scottish Parliament, First Minister John Swinney said the site was "iconic within the city".

"The efforts of SFRS were astonishing to avoid the spread of the fire from the building into the Central Hotel, as I will always call it, and Central Station," he said

"Although the site is devastating we have avoided a much greater incident by the skill and professionalism of the firefighters."

He said the government would "stand with the city of Glasgow" and would "back those words with cash".

"We will rebuild, we will restore, and Glasgow will flourish again," he said.

However, Swinney later said there would be difficult decisions on the remaining stone facade on Gordon Street.

"In the short term, there will be particular challenges about the stabilisation of what is a very vulnerable site to enable access at the earliest opportunity to Central station," he said.

What services are resuming?

The low level station is part of the Argyle Line, a cross-city rail link running under the city centre.

Services using it include those running from Balloch, Dalmuir, and Milngavie in the west, through to Motherwell, Larkhall, Lanark and Cumbernauld to the east

Low level services have not been stopping at Central since the fire, instead continuing onto Argyle Street also in the city centre.

Services from high-level platforms will remain disrupted, including:

Avanti West Coast said tickets dated between 8 -13 March can be used at no extra cost on any Avanti West Coast train on the same route until Friday, with services between Glasgow and London instead running from Motherwell or Edinburgh.

TransPennine Express said services between Glasgow Central and Liverpool Lime Street and Manchester Airport would not run on Tuesday.

The Caledonian Sleeper service from Glasgow Central to London Euston will begin its journey from Edinburgh, with complimentary connections from Glasgow Queen Street for ticket holders.

Union Street, where the fire took place, is a main drop-off point for many city centre passengers.

Police Scotland said several roads around Union Street and Central Station would remain closed. They are:

A warning has also been issued for drone operators wanting to access the airspace around the fire site.

A statement from Police Scotland said: "Drone pilots and operators are reminded it is an offence to fly over an ongoing emergency response and are encouraged to check NOTAM information and drone safety map before flying."

The SFRS said its response to the incident was scaled back on Tuesday with four fire engines and two high-reach vehicles still on site.

It confirmed the fire broke out in a vape shop and said a preliminary multi-agency investigation into the cause had begun.

Area commander Andy Kenna told BBC Scotland News officers were still damping down hotspots and it was "really difficult" to put a timescale on how long it would take to hand the site over to the local council.

He said the firefighters successfully put a break in to stop the blaze spreading to the station, but the gable end wall exposed on Central Hotel was being inspected by the council's building control team.

Susan Aitken, leader of Glasgow City Council, said the building was in a state of "ongoing and uncontrolled collapse".

"The top priority is public safety, but after that we want to get Central Station open as soon as possible," she told BBC's Radio Scotland Breakfast.

Aitken said she wanted to speak to the Scottish government and partners such as the Scottish National Investment Bank about how they can quickly help with "not just recovery but regeneration".

She said the majority owner of the building had made contact with the council.

Aitken said the council could "potentially expand on that existing work" and it was planning to reach out to the city's "developer and investor community" to discuss the future of the site.

The council leader warned about speculating on the cause of the fire, but said there needed to be a "wider discussion than just vape shops" about the storage and location of batteries - including those for mobile phones and e-bikes.