First South Yorkshire says the icy weather gripping the region means it is unable to operate a normal serrvice, with many buses terminating early or being diverted.
It said conditions are becoming worse and routes are having to be adjusted constantly.
Here are the First bus services affected as of 8.20pm this evening:
1a between Herdings and High Green: operating as normal but care required due to icy conditions on Blackstock Road
8/8a between Crystal Peaks and Parson Cross: operating as normal but care required due to icy conditions at Basegreen
18 between Meadowhall and Sheffield Interchange: diverted due to icy conditions in Meersbrook and Norton
18a between Meadowhall and Jordanthorpe: diverted due to icy conditions in Meersbrook and Norton
20 between Ecclesfield and Hemsworth: missing Meersbrook and Norton Lees due to icy conditions
29/29a between Harthill and Rotherham: operating as normal but Harthill terminus is described as very icy
35 between Hillsborough and Sheffield Interchange: Missing Jenkin Road and Wincobank Avenue
51/51a between Lodge Moor and Charnock: missing Charnock/Gleadless Common due to icy conditions
52a between Wisewood/Hillsborough and Woodhouse: operating as normal but care required at Beaverhill Road
56 between Wybourn and Herdings: Diverted - using Blackstock Road in both directions
81 between Dore/Millhouses and Stannington Nethergate: operating as normal but care required in Dore village where it is icy at the terminus
Stagecoach said its number 25 and 120 bus services in Sheffield were unable to serve the full route due to the icy conditions.
Number 25 buses are using Nodder Road in both directions, it said, and not serving Chadwick Road and Woodrove Avenue.
Number 120 buses, meanwhile, will terminate at the Old Fulwood Scout hut and will not serve Crimicar Lane, Hallamshire Road or Barncliffe Road.
There is a yellow weather warning in place for Sheffield and South Yorkshire today and throughout tomorrow.
The Met Office says heavy snow showers are expected in the region tomorrow, which may disrupt travel by road, rail and air. It warns that some rural communities could become cut off, there could be power cuts and mobile phone services may be affected.