An Irish state inquiry uncovered a "truly shocking" level of sexual abuse at religious schools, primarily those run by the Catholic Church, over nearly a century with 2,395 allegations, the government said on Tuesday.

The preliminary "scoping inquiry" found 884 alleged sexual abusers at more than 300 schools across the country between 1927 and 2013. Most of the cases occurred from the 1960s to the 1990s, the government said.

This step will be followed by a commission of investigation that is likely to find additional cases, Education Minister Norma Foley told a news conference.

"The level of abuse is shocking. It is truly shocking, and so is the number of alleged abusers," Foley said.

The preliminary inquiry was based on records held by religious institutions and the testimony of victims. It is the latest in a series of reports in recent decades into allegations of abuse and mistreatment by priests and members of religious orders, predominantly in Ireland's dominant Catholic Church.

The document is due to be published later on Tuesday after it is provided to victims.