Emergency services responded to a terror attack at Meadowhall as part of a training exercise overnight.
Over 856 volunteers were involved in the exercise, which was designed to test arrangements in place to respond to civil emergencies.
All of the county's emergency services were involved.
Deputy Chief Constable Mark Roberts, of South Yorkshire Police, said: “This was an extremely positive and useful exercise which tests our collective ability to respond to an emergency on a large scale.
"In this particular case, we chose to focus on a terrorism incident but this is not in response to a specific threat. The threat level to the UK remains at ‘severe’ as it has been since August 2014.
“The learning from today’s exercise will be fully debriefed and any learning will feed through to our policies, plans and procedures for the future.
“Today’s exercise was only possible due to the 856 volunteers who took part. I’d like to take this opportunity to offer my most sincere gratitude to them. They have played a key part in ensuring South Yorkshire remains a safe place to live, learn and work
“Although this was an exercise, the environment created is as realistic as possible. We saw officers and staff from each of the agencies, and members of the public carry out brave acts to secure the safety of others. It reminded us all why we do the job we do.”