Thousands gathered at Warsaw's largest square on Saturday for official ceremonies to honour the 96 victims of a plane crash that claimed the Polish president, politicians and most military brass.
A white cross stood at the centre of an altar set up on Pilsudski Square against a display of black and white photographs of the victims.
The crowd waved white and red Polish flags, and flags with the logo of the Solidarity labour union, which President Lech Kaczynski joined during Poland's communist rule. Shipyard workers from Gdansk, northern Poland, carried a flag depicting the Virgin Mary and Jesus.
Sirens rang out across the city at noon, followed by a moment of silence before names of the victims were read aloud and the national anthem was played.
The crash occurred in Smolensk, Russia, as the 96 were en route to ceremonies to mark the Soviet-era massacre of some 22,000 Polish officers, who were shot to the back of the head by Stalin secret police and buried in mass graves in the Katyn forest.
"The world crumbled for us for the second time, in the same part of the world," said acting President Bronislaw Komorowski. The tragedy was also a rare moment in history that united Poles, he added.
"None of us remembers a moment when so many, so many eminent people died in one horrible moment," Prime Minister Donald Tusk said. "Our deepest sense of unity, born in a moment of mourning, must last because then the deaths will have a significant, deep meaning."
Their speeches were followed by an outdoor mass in the square, at the site where Polish Pope John Paul II also gave a mass in 1979 that united thousands in the dark days of communism.
Sirens and church bells sounded across Poland at 8:56 am (1226 IST) to mark one week since the plane crash.
Buses, trams and the metro were free in Warsaw as a large block of downtown was shut down to traffic. Hundreds made their way from the central train station to Pilsudski Square, or gathered to watch the ceremonies on five large screens set up around the square.
The coffins of Kaczynski and his wife Maria are to be moved from the presidential palace, where they have been on public view since Tuesday, to Warsaw Cathedral for an evening mass.
Crowds continued to line up Saturday hoping to pay last-minute respects at the coffins. City officials said some 330 tons of burned-out candles and dried flowers have been removed from the entrance, reported the Polish Press Agency PAP. Hundreds of scouts were replacing them with new ones brought from Poles who came to Warsaw from across the country.
The Kaczynski coffins would later be transported to the southern city of Krakow for a state funeral Sunday. They are to be buried in Wawel Cathedral, in a sarcophagus near Jozef Pilsudski, who won independence for Poland in 1918 after more than a century of partitions.
The burial place sparked more controversy Friday as some 200 protesters gathered in Krakow saying the crypts, the traditional burial place of Polish kings, generals and national heroes, were too prestigious for the presidential couple.
The funeral in Krakow is to begin with a mass at St. Mary's Basilica. Relatives and heads of state would be seated inside, while thousands are expected to watch the mass outside on large screens.
The Berlin Philharmonic will play a concert - a gesture from the German government - to pay homage to the Kaczynskis.
Family members and heads of state will then form a funeral procession that will make its way up Wawel Hill, the ancient limestone outcrop that overlooks the Vistula River, to bury the couple in the Wawel Cathedral.
Russian President Dmitry Medvedev, US President Barack Obama and German Chancellor Angela Merkel are among those expected to attend the funeral in Krakow. Nearly 100 delegations, including a record number of world leaders, are expected to in Poland in time for the funeral.
Eight delegations have had to cancel because of the cloud of ash that has spread from an Icelandic volcano across Europe, the Poland's Foreign Ministry said Saturday.