They laid flowers and lit candles in front of the presidential palace. Many called the crash Poland’s worst disaster since World War II.

Two black boxes have been found and preliminary date indicated that the plane hit the treetops as it was making the approach to the airport in poor cisibility.

A week of mourning has been called in Poland where a two-minute silence will be observed at noon (1000 GMT) on April 11.

Prime Minister Donald Tusk said the crash was the most tragic event of the country's post-World War II history. He said the business of government would continue. The parliamentary speaker, Bronislaw Komorowski, has now become the acting president. He said he would, according to Poland's constitution, set the date for a presidential election after consulting with political parties.

The election must be held by late June, instead of the previously scheduled date of October.

Russia has also declared April 12 a day of mourning for the victims, whose remains have been flown to morgues in Moscow.

Russian Prime Minister Vladimir Putin said he would personally oversee the investigation into the crash. Mr Putin was joined by the late president's identical twin brother, himself a former prime minister, and Mr Tusk to lay wreaths at the plane's wreckage.

All bodies were recovered and were being taken to Moscow by helicopter for identification.

World leaders including Mr Putin, US President Barack Obama, German Chancellor Angela Merkel and UK Prime Minister Gordon Brown offered their condolences to Poland.