Former Chancellor Helmut Kohl, the architect of Germany's 1990 reunification and mentor to Angela Merkel, has died at age 87, his Christian Democratic Union party (CDU) said on Friday.

The mass-selling newspaper Bild reported that Kohl died on Friday morning in his home in Ludwigshafen, in western Germany.

"We mourn," the CDU tweeted with a picture of the former chancellor.

Germany's longest serving post-war chancellor from 1982 to 1998, Kohl was a driving force behind the introduction of the euro currency, convincing sceptical Germans to give up their cherished deutschemark.

An imposing figure who formed a close relationship with French President Francois Mitterrand in pushing for closer European integration, Kohl had been frail and wheelchair-bound since suffering a bad fall in 2008.

Tributes quickly flowed in from around the world.

Former U.S. President George H.W. Bush said he and his wife Barbara "mourn the loss of a true friend of freedom, and the man I consider one of the greatest leaders in post-war Europe."

"Working closely with my very good friend to help achieve a peaceful end to the Cold War and the unification of Germany within NATO will remain one of the great joys of my life," he added in a statement. "Helmut was a rock."