5:09 PM PT -- Nora has died. She was 71.
Nora Ephron -- the legendary Hollywood writer who penned the screenplays for "Sleepless in Seattle" and "When Harry Met Sally" -- is gravely ill ... family members are telling close friends.
The nature of her illness is unclear ... however there are reports she is suffering from cancer and is not expected to make it through the night.
There is speculation that Nora has already passed away -- we're told that's not true ... but there is little hope she will recover from her current condition.
71-year-old Ephron was nominated for 3 Academy Awards in her illustrious Hollywood career ... and was widely considered one of the most powerful women in the entertainment industry.
Among her most memorable films ... "Silkwood" ... "My Blue Heaven" ... "Michael" ... "You've Got Mail" ... and "Julie and Julia."
Ephron was married to (and famously divorced) Watergate scandal reporter Carl Bernstein ... before entering her 3rd (and final) marriage to screenwriter Nicholas Pileggi.