BERLIN: Chancellor Angela Merkel said Germany remains marred by division 20 years after the fall of the Berlin Wall as world leaders joined huge crowds toasting a free Europe.

"German unity is still incomplete," said Merkel, who grew up behind the Iron Curtain in communist East Germany.

"We must tackle this problem if we want to achieve equal quality of life" in east and west, she told ARD public television, noting that unemployment was still twice as high in the depressed east than in the west.

Merkel was to host Britain's Prime Minister Gordon Brown, presidents Nicolas Sarkozy of France and Dmitry Medvedev of Russia and US Secretary of State Hillary Clinton at the Brandenburg Gate, once on the fault line between East and West Berlin.

Former Soviet leader Mikhail Gorbachev, ex-Polish president Lech Walesa and dissidents who helped rip down the Wall and end European communism will also be on hand at the former "death strip" where border guards had shoot-to-kill orders.

At a ceremony late on Sunday kicking off official festivities, Clinton issued a call for a new transatlantic push to free those still oppressed.

"Our history did not end the night the Wall came down," she said.

"To expand freedom to more people, we cannot accept that freedom does not belong to all people. We cannot allow oppression defined and justified by religion or tribe to replace that of (communist) ideology."

On the night of November 9, 1989, following weeks of pro-democracy protests, East Germany's Stalinist authorities suddenly opened the border.

After 28 years as prisoners in their own country, euphoric East Germans streamed to checkpoints and rushed past bewildered guards, many falling tearfully into the arms of West Germans on the other side.

In a tribute to be delivered at the Brandenburg Gate, Brown called the unity of Berlin, Germany and Europe "majestic" achievements.

The Wall "was swept away by the greatest force of all -- the unbreakable spirit of men and women who dared to dream in the darkness," he said.

Sarkozy shared his own memories of November 9 on his Facebook page, saying he had been in Berlin and was among the first to chip away at the Wall's concrete slabs.

"We then headed for Checkpoint Charlie (border crossing) to see the eastern side of the city and finally confront this Wall and I was able to take a pickaxe to it," he wrote.

Russian Prime Minister Vladimir Putin, who was a KGB agent in Dresden under communism, said he had fond memories of East Germany including learning German, mountain excursions and contacts with local agents.

"But we see how the Federal Republic (united Germany) is developing and we are happy that we have good relations on a new basis," he said. "This of course makes any nostalgia secondary." Putin's 'nostalgia' for East Germany

Merkel, Walesa and Gorbachev, who remains a revered figure here, will join former dissidents in crossing the former checkpoint at Bornholmer Strasse, where hundreds of East Germans had their first taste of freedom.

The celebrations will later move to the Brandenburg Gate for an open-air concert and the symbolic toppling of 1,000 giant styrofoam dominoes along two kilometres (1.2 miles) of the Wall's former course.

An overwhelming majority of Germans are still grateful for the Wall's fall, according to a poll in the Leipziger Volkszeitung daily, with 79 percent of those surveyed calling November 9, 1989 a joyous day.

But sociologist Frithjof Hager of Berlin's Free University said national unification, sealed in 1990, was still a work in progress.

"I believe the authoritarian mindset is still an issue (in the east) -- such things only change very slowly," he told AFP. "But I think simply pointing the finger at easterners would be deeply unfair."

South Korean activists marked the anniversary in Seoul by launching leaflets attacking North Korea's leader across the world's last Cold War frontier.

"Down with Kim Jong-Il's Songun dictatorship," they shouted in reference to the leader's army-first policy which prioritises the welfare of troops over civilians.