Queensland prisoners in mass overdose

One prisoner remains in hospital and five others have been returned to custody after a suspected mass drug overdose in a Queensland prison.

Part of the Capricornia Correctional Centre remains in lockdown after paramedics were called in about 12.40pm on Sunday.

Queensland Corrective Services says the inmates' cells have been secured as crime scenes and a full search is underway.

"CSIU are co-ordinating with local police to interview prisoners to attempt to identify the source of the illicit substance," according to its statement.

"If the source is identified, they risk a two-year prison sentence.

"We regularly undertake random searches within the prison for contraband. Sadly people go to extraordinary lengths to evade these efforts."