The crowd in Pilsudski Square waved white-and-red Polish flags with black ribbons of mourning affixed to them. A massive white stage, a large cross in the center, was flanked by oversized photos of the dead, including President Lech Kaczynski.

The names of the dead were read aloud, starting with the president and his wife, Maria, while Marta, their only child, and Jaroslaw Kaczynski, the president's twin brother and former prime minister, looked on. Others at the service included former President Lech Walesa, Prime Minister Donald Tusk and acting president Bronislaw Komorowski.

"Our world went crashing down for the second time at the same place," Komorowski said of the crash near Russia's Katyn forest, site of a World War II massacre of Polish officers.

Tusk called the crash a calamitous event that was "the greatest tragedy in Poland since the war."

The ceremony is the first of two days of ceremonies and will be followed by a funeral Mass for the first couple at St. John's Cathedral at 6 p.m. (1600 GMT; noon EDT) in Warsaw.

Among the mourners was Teresa Winkler, 76, who came to honor a president "who took care of the people forgotten by society," such as aging World War II soldiers and forgotten Solidarity activists.

"He was a real patriot and a real Pole," Winkler said. "I am afraid it will be hard to find another president like Kaczynski."

Nearby was a group of Chechen refugees who said they were there to honor the first lady for her charity work and efforts to help them.

Members of Solidarity, the freedom movement that Kaczynski supported and that still exists as a labor union, waved their banners.

A state funeral for the president and his wife is set for Sunday but some world leaders canceled their plans to go, citing the volcanic ash cloud hanging over Europe, leaving numerous airports closed.

So far delegations from India, Japan, South Korea, Mexico, New Zealand and Pakistan have canceled plans to attend Sunday's state funeral, Polish Foreign Ministry spokesman Piotr Paszkowski said. Poland said it still expects nearly 100 dignitaries, including President Barack Obama and Russian President Dmitry Medvedev.

Czech President Vaclav Klaus said he would travel to Krakow by train and car while Slovak President Ivan Gasparovic said he would go by car.

Last Saturday's crash plunged Poland into a deep grief not seen since the death of Pope John Paul II five years ago.

The city operated buses and subways for free and the government banned the sale of alcohol until Saturday night.

"What happened was a great shock for us; we are here today though we didn't like many of the things that those who died represented," said Maciej Gajewski, a 40-year-old engineer who was there with his wife and three children.