Czech citizens joined their leaders and foreign politicians Sunday in paying tribute to Vaclav Havel, the dissident playwright who led the 1989 Velvet Revolution that peacefully toppled communism in the former Czechoslovakia.

A black flag flew over Prague Castle, the presidential seat, while Czechs lit candles at the monument to the revolution in downtown Prague in memory of Havel, who died earlier Sunday at the age of 75.

"Mr. President, thank you for democracy," read a note placed there.

Others came to Havel's villa in Prague to lay flowers and light candles.

Josef Klik, a 67-year-old, was among the mourners.

"He is an unforgettable person who contributed to the fall of communism," Klik said. "And after that, he remained a moral authority for ordinary people."

At downtown Wenceslas Square, where Havel talked to hundreds of thousands during the 1989 revolution, an impromptu gathering of mourners was planned for late Sunday.

Canadian Prime Minister Stephen Harper hailed the artist and ex-politician as "one of the great statesmen of the 20th century and a powerful voice for freedom and human dignity," in a statement released late Sunday.

"The world owes a great debt to Václav Havel," concluded Harper's statement. "In helping to free his own people he helped spread freedom across an entire continent ,and showed us all that even an evil dictatorship can be no match for the power of the human spirit."

Former Canadian prime minister Jean Chrétien, who met with Havel several times, said he would be remembered as someone who took all the talent he had and used it to make a better place for his people, at great risk to himself. 

"He was a great champion of freedom," Chrétien told CBC News Now host Nancy Wilson on Sunday. "And he was a very courageous writer who was a champion of the liberation of the people who were under the control of the Soviet Union."

Vaclav Klaus, Havel's political archrival who replaced him as president in 2003, called Havel "the symbol of the new era of the Czech state."

Foreign Minister Karel Schwarzenberg added that Havel "returned dignity to the Czech nation."

In neighbouring Poland, the founder of the anti-communist Solidarity movement and former president Lech Walesa called Havel "a great fighter for the freedom of nations and for democracy."

"It is a great pity and a great loss. His outstanding voice of wisdom will be missed in Europe," said Walesa, the 1983 Nobel Peace Prize laureate.

"We have lost a great leader," former U.S. Secretary of State Madeleine Albright, who is of Czech origin, said in a statement sent to the AP.

"Vaclav Havel leaves our world better for having been a part of it," Albright said. "My thoughts and prayers go out to his wife Dagmar Havlova, his family and the people of the Czech Republic."

'Led Czechs out of tyranny'

British Prime Minister David Cameron said, "Havel led the Czech people out of tyranny. And he helped bring freedom and democracy to our entire continent."

The Czech government meets Monday to declare a period of official mourning. Klaus said condolence books will be available for people to sign at the Prague castle, the presidential seat, starting Monday for people to sign.

In Slovakia, which split from the Czech Republic in 1993, Prime Minister Iveta Radicova said it was Havel who "opened the gates to the world after 1989."

German Chancellor Angela Merkel, who grew up in East Germany and went into politics as communism crumbled, said she learned "with great dismay" of Havel's death.

"His dedication to freedom and democracy is as unforgotten as his great humanity," Merkel wrote in a message to Klaus. "We Germans also have much to thank him for. Together with you, we mourn the loss of a great European."

The president of the European parliament Jerzy Buzek — a former Polish prime minister and activist in Solidarity — wrote on Twitter: "Vaclav Havel is the figure that represents the Velvet Revolution and the reunification of Europe. He will be sorely missed."

Swedish Foreign Minister Carl Bildt tweeted that Havel was "one of the greatest Europeans of our age."

He added on his blog that Havel was "maybe the strongest voice from behind the iron curtain that no longer accepted a Europe divided between freedom and repression."

In Russia, Grigory Yavlinsky, a veteran opposition figure and leader of the Yabloko party, told the Itar-TASS news agency that Havel "was a man of integrity and dignity who has never been afraid of anyone."

"He devoted his life to freeing his people from a totalitarian regime," Yavlinsky said.

With files from CBC News