Firefighters were called to an arson attack in the Peace Gardens in Sheffield city centre.
A pile of cardboard was set alight at 9.55pm last night.
Crews also dealt with rubbish set on fire in Coppice Road, Highfields, Doncaster; a blaze in woodland off Hollings Lane, Ravenfield, Rotherham; conifer cuttings set alight in Margetson Crescent, Parson Cross, Sheffield and a fire in the open off Yews Lane, Kendray, Barnsley.
A South Yorkshire Fire and Service spokesman said: "“All acts of arson are treated extremely seriously, we are working closely with South Yorkshire Police to identify those responsible and to prevent any further instances occurring.
"Incidents such as these take up a large amount of our resources when they could be needed at genuine life-threatening emergencies.
“These small fires have the potential to spread and could put lives at risk."
Anyone with any information should call police on 101 or Crimestoppers on 0800 555111.