Bosses at security firm G4S, which runs HMP Oakwood in South Staffordshire, have put contingency plans in force as a rooftop protest continues at the prison.
A spokesman confirmed six prisoners were involved in the incident.
We can confirm that an incident involving six prisoners is taking place at HMP Oakwood.
The Ministry of Justice has been alerted and our normal contingency plans have been enacted.
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Witnesses who saw the incident said that the man threw the dog in the air a number of times and let her drop to the floor.
Very windy across northern areas this morning. Feeling fresher.
Dry, some sunshine and lighter winds.