All the world from the Sydney Opera House to the Empire State Building turned Irish, or at least Irish for the day, as revelers marked St. Patrick's Day with bagpipes, dancing, emerald lights and green body paint in a flurry of celebration.

New Yorkers and visitors from all over the globe lined Manhattan's Fifth Avenue a dozen deep for the world's oldest and largest St. Patrick's Day parade Wednesday, as crowds gathered along sun-warmed routes in Dublin and cities around the U.S. to mark the holiday.

The day simultaneously served as a celebration of spring in many cities, with participants in parades and other outdoor gatherings basking in temperatures in the 60s after a harsh winter.

The 249th St. Patrick's Day extravaganza in New York City was to be the last of the Big Apple's world-famous parades to take place before new restrictions go into effect April 1 requiring all parades to be shorter to save money.

The city issued the new rules in February, requiring all parades to trim routes by 25 percent and reduce time to less than five hours, changes estimated to save US$3.1 million in police expenses.

St. Patrick's celebrations around the country and in Dublin featured threads of the same bagpipes, marching bands and crowds eager to see spring weather.

There was a mix of lighthearted cheer and serious politics at the White House, where U.S. President Barack Obama met with Irish Prime Minister Brian Cowen.

Obama noted that 36 million Americans claim Irish ancestry, adding, “I'm sure more do on St. Patrick's Day.”

As part of a marketing deal by Ireland's tourism agency, major world landmarks including the Sydney Opera House, the London Eye, Toronto's CN Tower and New York's Empire State Building were bathed in green lights.

The day is named after St. Patrick, who introduced Christianity to Ireland about 1,500 years ago and became the country's patron saint.

More than half a million people lined the 2-mile route of the flagship Dublin parade, which had a theme this year celebrating the global spread of the Irish.

Mixed in with the usual displays of U.S. marching bands and Irish sporting heroes were dancing troupes from Africa and India, bands from Austria and France, giant insect floats from Spain, and Dubliners dancing with mops and dusters.