He had reportedly been due to attend his mother's 90th birthday celebrations later in the day.
"For us this is the end of the world," the deputy leader of Mr Haider's Alliance for Austria's Future, Stefan Petzner, told Austrian news agency APA.
Austria's President Heinz Fischer said Mr Haider's death was a "human tragedy", while Chancellor Alfred Gusenbauer described him as someone who had shaped Austria's domestic and political landscape over decades, according to the Associated Press news agency.
Mr Haider was a divisive figure who gained notoriety after he became leader of the Freedom Party in 1986.
In 1991 his term as governor of the province of Carinthia was interrupted, after he made comments praising employment policies of Nazi Germany.
Mr Haider speaking about immigration in September
But he was re-elected in 1999 and 2003.
In 2000 the EU imposed sanctions against Austria in a protest over his party's role in government.
In 2005 Mr Haider left the Freedom Party and founded the Alliance for Austria's Future, which scored its best result so far in elections last month, gaining 11% of the vote.
This was, however, well below the 27% which the Freedom Party won under his leadership in 1999 - a high mark in Mr Haider's electoral career at national level.
"With his passing Austria has lost a great political figure," said Heinz-Christian Strache, who had taken over as leader of the Freedom Party after Mr Haider left.
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