People.com said Richardson was initially taken to a hospital near the luxury Mont Tremblant ski resort in Quebec, and was later transferred to the Montreal hospital.
A family member confirmed Richardson had had a skiing accident.
"We know that she has had an accident but we really do not know any more details," said Kika Markham, who is married to Richardson's uncle, Corin Redgrave. "We are very concerned."
Richardson, 45, is the elder daughter of Oscar-winning actress Vanessa Redgrave and the late director Tony Richardson, and belongs to a British acting dynasty.
Her maternal grandparents were the actors Michael Redgrave and Rachel Kempson, and her uncle Corin and aunt Lynne Redgrave are also both actors. Sister Joely Richardson is also an actress, best known for starring in TV series "Nip/Tuck."
Richardson's films include "Gothic," "A Month in the Country," "Nell"
-- in which she appeared with future husband Liam Neeson -- "The Parent Trap" and "Maid in Manhattan."
Trained at London's Central School of Speech and Drama, Richardson has had extensive stage experience in the West End and Broadway. She won a Tony Award in 1998 for playing Sally Bowles in "Cabaret."
In January, Richardson and her mother played the roles of mother and daughter in a one-night benefit concert version of "A Little Night Music," the Stephen Sondheim-Hugh Wheeler musical, at the Nokia Theatre Times Square in New York.
She married Neeson in 1994, and the couple has two sons.