A 150-year-old staircase collapsed at Ireland's Natural History Museum on Thursday, injuring a group of elementary school teachers — 11 of whom were hospitalized, officials said.

The 21 teachers on a "science appreciation course" were touring the museum when a limestone staircase fractured and crumbled from their weight, Culture Minister Seamus Brennan told the Irish parliament.

The victims fell less than a story to the ground floor, Dublin fire department spokesman Greg O'Dwyer said.

The victims were hospitalized at three Dublin hospitals with injuries that did not appear life-threatening. Several other teachers were treated at the scene for minor cuts, scrapes and bruises.

The building will be closed to both visitors and staff for several weeks while health and safety officials inspect it for other potential dangers, said Pat Wallace, director of the National Museums of Ireland.

The staircase dates back to the construction of the building, which opened in 1857, making it the oldest purpose-built museum in Ireland.

The museum displays about 10,000 animals, including examples of long-extinct species, from a wider zoological collection of 2 million specimens dating back to the 18th century.