A MONET painting worth up to €30m was badly damaged at the National Gallery when a man punched a hole in it.
He had been in the building for less than five minutes.
Argenteuil Basin With A Single Sailboat, painted in 1874, is being examined by the gallery's conservation staff.
Witnesses said the man, in his 40s and 'heavy-set', arrived at the Merrion Square gallery shortly before 10.50am yesterday morning and had been walking around before puncing the painting.
The man, dressed in jeans and a blue T-shirt, tried to leave the gallery and became agitated when he was apprehended by security staff, who held on to him until gardai arrived.
"He was taken away in an ambulance; a garda travelled with him," one witness told the Herald. The man made no statement about why he had damaged the painting and it was not known if he had singled it out or if it was a random attack.
The painting, which measures 55 x 65 cm, was removed from view and brought to the conservation staff.
Gardai and security chiefs at the gallery are also examining CCTV footage of the attack, which was caught on camera.
A spokesperson for the National Gallery said there was no commercial value on the painting because it forms part of the state collection.
However, in 2008 Monet's Le Bassin Aux Nympheas sold for just over $80m (¤63m) in New York. Also in 2008, Monet's The Railroad Bridge at Argenteuil sold for $41.4m (€32.7m) at Christie's in New York.
The painting has been removed for assessment.
"The NGI does not have any more details about the incident as the matter is now with the gardai," a spokesman said.
"It is a shocking and very regrettable incident and I would like to praise the Garda Siochana and the NGI staff in dealing promptly with the matter," said Sean Rainbird, director of the National Gallery of Ireland.