Joni Mitchell is reportedly in intensive care in Los Angeles.
The 71-year-old singer was rushed to hospital by paramedics on Tuesday after they received a 911 call from her home.
A source told gossip website TMZ.com that the caller claimed a female was unconscious, but alert.
It is not yet known what the 'Big Yellow Taxi' hitmaker is being treated for.
Last year, Joni, who was inducted into the Rock and Roll Hall of Fame in 1997, admitted she endured years of turmoil after being diagnosed with the rare condition Morgellons disease, which made her believe parasites were living under her skin.