Ambulance crews had to use 4x4 vehicles to cover the Forest of Dean area after heavy snow fell in the area.
Gloucestershire Ambulance Service said it was proving difficult to get to all areas and appealed for people only to call if absolutely necessary.
A police spokesman said some roads in the Forest were blocked and described the road conditions as "treacherous".
"Vehicles stuck in the snow are making it difficult for snow ploughs to clear the roads," Supt Nigel Avron said.
'Stay with friends'
Supt Avron added: If you're working somewhere such as Gloucester or Cheltenham and can stay with relatives or friends tonight, please do so rather than try to get home.
"If you do have to drive, please go very slowly and leave plenty of distance between you and the vehicle in front," he said.
On Friday evening the Highways Agency were advising drivers of heavy snow and ice on the A40 in Gloucestershire between the A4136 junction at Huntley and Lea Lines.
Heavy traffic and parked cars on the A48 were also preventing gritters from covering the area.
On Friday evening a Met Office spokesman said: "The sleet is expected to die-out before midnight but the dual hazards of ice and fog may well hamper recovery efforts for a time before further sleet or snow returns later in the night.