Berlin  - German Chancellor Angela Merkel on Saturday expressed thanks to Hungary for its opening of its border with Austria 20 years ago, triggering the start of the collapse of communism in Europe.

In her weekly video address, Merkel commented on the "Pan European Picnic" of August 19, 1989 when part of the border fence separating Hungary from Austria was opened, with hundreds of East Germans immediately taking the chance to flee to the west.

"This made the opening of The Wall irreversible," Merkel said, referring to the main symbol of Europe's - and Germany's - post-war division, the Berlin Wall.

Merkel is to visit Hungary next Wednesday to mark the 20th anniversary occasion.

"My trip is a thank-you to Hungary - to the people who live there and also to those who were then responsible," she said, referring to Hungary's then-communist rulers who permitted the border opening. They had shown courage and foresight and thereby had accelerated the cause of democracy in Central and Eastern Europe, Merkel added.

"Today we have the task of assuring that young people who live in freedom and are growing up with free borders, should know that this freedom must be fought for," said Merkel, who 20 years ago was herself a citizen of then-communist East Germany.

Merkel and Hungarian Prime Minister Gordon Bajnai are to participate jointly in the August 19 anniversary festivities. In the town of Sopron the German chancellor will meet with eyewitnesses to the events then. That evening, she is to attend a concern with Hungarian President Lazlo Solyom. (dpa)