Trains have been delayed and cancelled after an exclusion zone was extended around Ayr station.
Contractors found crumbling and exposed roof areas at the former Station Hotel next door.
Councillors said the problems "present a significant and immediate danger to people and places around the station".
No services are running between Ayr and Girvan and there is a reduced service between Ayr and Glasgow Central.
It is unclear how long the rail disruption is expected to continue for.
ScotRail has refused to comment on reports that the station could be closed completely from Sunday.
The company has apologised to customers and detailed the changes to services on its website.
Speaking earlier on the BBC's John Beattie radio programme, Angus Thom, ScotRail's chief operating officer said: "We are not able to access the full length of all the platforms at Ayr station.
"This means that we can't get the length of trains that we usually operate, which are as long as seven carriages, into the station.
"The maximum length of train we can operate from the station is four carriages long."
Mr Thom also advised visitors to the Scottish International Airshow this weekend to seek alternative transport.
He said trains would be running over the two days, Saturday and Sunday, but at a reduced capacity.
"We will put in as many trains as we can into Ayr station, but what I would encourage people to do is look at other forms of transport where they can," he said.
"Our plans for Ayr airshow will be publicised on our site. My advice to people would be plan your journey, and take extra time.
"If you can use something other than the railway, we'd like you to consider that. But we will be running trains."
'Failure to address concerns'
In March, South Ayrshire Council issued the owner of the Station Hotel with a dangerous buildings notice demanding action but it said there had been "no meaningful dialogue".
An exclusion zone was set up around the building in the summer.
The B-listed hotel, which dates to 1885, was built by the Glasgow and South-Western Railway Company, according to the Buildings at Risk Register for Scotland.
The council said it was working closely with Network Rail and ScotRail as work progresses to address the dangers presented by the hotel.
Eileen Howat, chief executive of South Ayrshire Council, said: "Unfortunately, we're having to take urgent action to extend the exclusion zone in place at the station after contractors identified crumbling and exposed roof areas that present a significant and immediate danger to people and places around the station.
"This is not action that anyone is taking lightly, but is wholly designed to keep people safe, and not put them at risk as a result of the failure of the private owner of the building to address the safety concerns we have highlighted time and time again.
"Network Rail and ScotRail have been fully involved in the discussions about this and - as a result - a reduced service will be operating between Glasgow Central and Ayr, supported by rail replacement buses.
"Our priority right now is to continue to work with Network Rail and ScotRail to keep their passengers, staff and the public safe, before continuing discussions regarding the next steps that need to be taken to address the dangers of the Station Hotel building."