Five medieval mummies preserved in the crypt of a Dublin church have likely been damaged beyond repair by a fire and water used to douse the flames, a church official said on Wednesday.

The five sets of remains, preserved for hundreds of years in the crypt of the 11th century St. Michan's Church in central Dublin, include the remains of a crusader and are a tourist attraction in the city.

An intruder broke into the crypt on Tuesday afternoon and started the fire and firefighters used water to put it out, the Church of Ireland Archbishop of Dublin, Michael Jackson, told RTE radio.

"The combination of fire and water have done significant damage to the mummies... I honestly don't know exactly what the extent of that is, but my fear like that of others is that the damage is irreparable," Jackson said.

The remains are due to be examined by experts from the National Museum of Ireland to see if anything can be salvaged, he said.

The vicar of the church, David Pierpoint, told RTE he thought the mummies were "beyond repair".