People attend a national memorial service in Warsaw's Pilsudski Square on Saturday. (Markus Schreiber/Associated Press)Some 100,000 Poles filled Warsaw's main square Saturday for a memorial to the 96 people killed in a plane crash in Russia a week earlier, standing silent for two minutes before emergency sirens screamed and church bells pealed.

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 centre, 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 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.

Supporters of the late Polish president hold a poster prior to a national memorial service in Pilsudski Square. (Ferdinand Ostrop/Associated Press)

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 honour a president "who took care of the people forgotten by society," such as aging Second World War 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 honour the first lady for her charity work and efforts to help them.

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

Nuns and other women attend the national memorial service. (Alik Keplicz/Associated Press)

So far delegations from India, Japan, South Korea, Mexico, New Zealand and Pakistan have cancelled plans to attend Sunday's state funeral, Polish Foreign Ministry spokesman Piotr Paszkowski said.

Poland said it still expects nearly 100 dignitaries, including U.S. 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," Maciej Gajeewski, a 40-year-old engineer who was there with his wife and three children.

"But we are sorry for them. I feel like a Pole here, I feel united with my compatriots in this difficult situation," he said.

Dignitaries were to attend Katyn memorial

On Sunday, numerous world leaders are expected for a tradition-laden funeral for Kaczynski and his wife, whose plane went down in heavy fog after clipping a birch tree on approach to Smolensk, Russia.

Those aboard the plane had planned to attend a memorial for thousands of Polish army officers executed in the Katyn forest in 1940 by the Soviet NKVD secret police.

All airports in Poland remained closed Saturday to flights above the cloud level of 6,000 metres (20,000 feet) because of the ash cloud, including Balice in Krakow where most of the dignitaries are expected to arrive on Sunday morning, said Grzegorz Hlebowicz, spokesman for Poland's aviation authorities.

South Korean Prime Minister Chung Un-chan cancelled his trip and the Polish news agency PAP reported that Cardinal Angelo Sodano, dean of the College of Cardinals, could no longer fly from Rome to deliver a memorial mass there.

Sunday's state funeral in mostly Roman Catholic Poland will begin at 2 p.m. local time (8 a.m. ET) with a mass at the 13th-century St. Mary's Basilica.

The bodies of the late president and his wife will then be carried in a funeral procession across the Old Town to the historic Wawel Cathedral, where they will be interred.