PUBLIC safety fears closed Truro Bus Station on Monday as "subsidence issues" required emergency repairs.
Bus services were disrupted and passengers were rerouted across the city as the exit to the station was cordoned off around a large hole in the brick surface.
A group of drivers stood across the entrance to the station in a line.
A handwritten sign said: "Owing to urgent repairs to the entrance of this bus station please consult the departure sheets on windows. We are sorry for the inconvenience this has caused."
Bus operator First Devon and Cornwall said "subsidence issues" posed a risk to their buses, which instead picked up passengers from Green Street, Lemon Quay and Haven House.
Richard Taylor, of Cornwall Council's highways department, said the station had been looked at the previous week and it was decided that urgent work was needed as "it had become a safety issue".
He said sand is moving around underneath the surface bricks leaving them uneven but tests on Monday found the foundations were "properly engineered up through and seem to be fine".
"When we dug the bricks up in one particular spot there was no sand left," he said.
"It's not right or what we would expect to happen but the bus station hasn't got to be moved because of this issue."
The hole has been filled with tarmac, the same solution used in other parts of the station in the past.
"It's a quick fix to get it done while we run the buses," said Mr Taylor. "Keeping the station in operation is all about safety. Lots of patching has been done over the years.
"The temporary repairs have held up before but now it's looking patchy.
"It's safe enough. Whether it gets worse or not is the big issue.
"We need to do some more testing and people are looking at the options of what we can do."
Engineers are still puzzled about what is causing the problem.
Mr Taylor said: "The buses are big vehicles and the problem might be caused by the way they move. The station has been there a reasonable time so the frequent bus movements will make a difference.
"We have got some ideas about what could be causing it but we don't really know."