Nine prisoners, including at least one who is in a critical condition, have been rushed to hospital after suspected overdoses at Portlaoise Prison in the Republic of Ireland.

The incidents happened this afternoon on the C wing in the midlands prison, which houses a number of convicted killers and gangland criminals.

Six inmates were initially brought to hospital while a further three were hospitalised later this afternoon.

Prison sources say that illicit drugs have been “retrieved” from C wing and have been sent for testing.

It is too early to determine what type of drug was used. Portlaoise is Ireland’s highest security prison.

In a statement, the Irish Prison Service said it is working closely with the HSE and it has secured extra naloxone kits in the event of clinical intervention.

“Extra vigilance is being taken across the prison estate and the Irish Prison Service has commenced an information campaign for prisoners around the dangers of consuming contraband.

“The Irish Prison Service is committed to preventing the access of contraband including drugs into prisons and continues to be a high priority for the Irish Prison Service. The Irish Prison Service has committed to continuing to invest in new technologies and measures to support our efforts to keep contraband out of prisons.

It said prison staff have increased the use of “random and intelligence led cell searches on a daily basis”.

“Our Canine Unit carry out searches around the prisons, including a greater focus on searching deliveries into prisons.

“The Irish Prison Service continues to engage with An Garda Síochána with regard to preventing contraband entering our prison and this happens at both local and national level. The Operational Support Group work closely with their colleagues in An Garda Síochána on a regular basis and the sharing of intelligence has led to target searches resulting in the seizure of contraband.

“The Irish Prison Service are committed to strengthening our measures in keeping drugs out of prison and in this regard a new drug strategy was published last November.”

Last month, the Irish Prison Service issued an urgent drug alert to all prisons after an analysis by the HSE’s National Drug Treatment Centre confirmed the presence of a nitazene-type substance called N-Pyrrolidino protonitazene – which has been associated with the overdoses in custody.

It is a very strong and potentially deadly synthetic opioid and has been appearing across the country since June.

The tablets often come in blister packs and are often yellow in colour. People could easily mistake them for benzodiazepines.

However, the nitazine tablets do not contain benzodiazepine and are unsafe to use. Nitazine is a synthetic opioid.

The Irish Prison Service sent a protonitazene tablet to the HSE lab after they had an overdose in one jail.

The lab found it was the same type as the one they had begun to see in Ireland since June.