Ten prisoners have been rushed to hospital following a suspected mass drug overdose at Portlaoise Prison.
The Irish Prison Service says it is working closely with the Health Service Executive (HSE) in response to the incident.
One of the prisoners is believed to be in a critical condition. The condition of the others has been described as serious.
A quantity of white powder was found and has been sent for analysis.
The Irish Prison Service says it has secured extra naloxone kits.
These are used to temporarily reverse the effects of opioid drugs like heroin, morphine, codeine and methadone.
Extra vigilance is being taken across the prison estate and an information campaign has begun to warn prisoners of the dangers of consuming contraband.
In a statement, the Prison Service says staff have increased the use of random and intelligence-led cell searches on a daily basis.
It adds that increased focus is also being put on searching deliveries into prisons.
