German President Frank-Walter Steinmeier has honoured former chancellor Angela Merkel as a "role model and a hallmark of our democracy” ahead of her 70th birthday.

"The special thing about this anniversary is that your 70 years of life can be divided into exactly two halves. The first 35 years until the fall of the Berlin Wall and the second 35 years in the freedom you longed for,” Steinmeier wrote in a birthday message.

In the second 35 years, Merkel had decisively shaped the path of a united Germany as chancellor, he said. (DPA)