Updated with video.
Just in from the Kraftwerk fan-list:
I have just come from the Global Gathering concert in Melboourne where
Kraftwerk were to have played tonight.
Unfortunately the performance was cancelled and a very shocked looking
Ralph came onstage to let everyone know that Fritz had suffered 'heart
I know nothing more at this stage.
My thoughts are with his family and the other members of Kraftwerk
From Wikipedia: Fritz Hilpert replaced Wolfgang Flür in concert when Kraftwerk resumed their touring activities in 1990, and engineered the album The Mix, released in 1991. He has made musical contributions to Kraftwerk's compositions since Expo 2000 in 1999. Along with Henning Schmitz he works as sound engineer at Kling Klang studio and is administrator of the Kraftwerk.com and Klingklang.com websites.