Though not unexpected (since we all share mortality and he had been in failing health) sadness nonetheless prevails. The Dorstener Zeitung has the report.
Einer der weltweit bedeutendsten Experten für die Literatur des Urchristentums und antiken Judentums, Prof. Martin Hengel, ist am Donnerstag in Tübingen gestorben. Der evangelische Theologe wurde 82 Jahre alt, teilte die Württembergische Landeskirche in Stuttgart mit.
He was too young, so far as I’m concerned. His work played a terribly significant role in my theological / exegetical development and he will be missed by all of us [originally published at 6:16 pm on July 2].

UPDATE: Doug Chaplin and James Spinti too have noted this sad news. Others will in due course no doubt, because Hengel was so very important.
UPDATE II: The Esslinger Zeitung has the story now (with the same info). As other news outlets, with other details, come to notice, I’ll update the listing and the timestamp.
UPDATE III: Sean Winter has written a very nice, very clear appreciation of Professor Hengel. It’s very much worth seeing. Thanks, Sean. I think all of us who made the time to read Hengel were and will remain impressed by him. I know I shall.
UPDATE IV: This Italian report contains no new information, but it does have this more recent photo of Professor Hengel.

UPDATE V: A snippet of a comment from one of Hengel’s colleagues has appeared here.
»Martin Hengel war ein großer theologischer Lehrer unserer Kirche«, sagte Landesbischof Frank Otfried July während der Sommertagung der Württembergischen Evangelischen Landessynode. »Er war für viele Studierende Gestalt der neutestamentlichen Forschung.« Hengel habe einen großen und unverwechselbaren Beitrag zur neutestamentlichen Forschung und darüber hinaus geleistet. Zum Gedenken an den Theologen legten Bischof und Synode eine Schweigeminute ein.
UPDATE VI: Ken Schenck has posted some really fine anecdotes from his own encounters with Professor Hengel here. Thanks for doing that Ken.