Varying reports swirled about her condition - some saying she was seriously hurt.
IrishCentral.com reported that the wife of Liam Neeson was in critical condition with a head injury.
In Los Angeles, a person close to the family, who asked not to be identified because of the sensitivity of the matter, confirmed that Richardson landed in New York after leaving Montreal's Sacre-Coeur hospital in the afternoon, where she was treated after falling during a private lesson Monday at the famed Mont Tremblant ski resort.
The person did not say if or where the actress was being treated in New York.
Richardson, 45, is the elder daughter of Oscar-winning actress Vanessa Redgrave and the late director Tony Richardson, and belongs to the British acting dynasty.
"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."
A statement from the Mont Tremblant resort said Richardson fell on a beginners trail and later reported not feeling well.
"She did not show any visible sign of injury but the ski patrol followed strict procedures and brought her back to the bottom of the slope and insisted she should see a doctor," said the statement from the resort, about 80 miles northwest of Montreal.
The ski resort said the instructor and a member of the ski patrol accompanied Richardson to her hotel, where they again recommended she should be seen by a doctor.
"An hour later she said she didn't feel well. She had a headache, so we sent her to the hospital," Lacasse said. "There were no signs of impact and no blood, nothing."
An ambulance was called and Richardson eventually was transferred to Sacre-Coeur hospital in Montreal.
The fall could have caused one of several brain injuries, say doctors who deal with head trauma.
Little was known late Tuesday about her condition or the extent of her injuries.
However, doctors not involved in her case but experienced with head trauma say her reported symptoms are consistent with a blood clot in or around the brain, which can occur when a blow to the head or neck causes one or more blood vessels to rupture.
"There are at least two major conditions that can happen after a head injury," said Dr. Charles Tator, a neurosurgeon at Toronto Western Hospital. "One is the development of a blood clot. And the blood clot could form inside the brain tissue itself or between the skull and the brain."
Tator, stressing he cannot speak directly to Richardson's case, said such falls can cause a blood vessel to tear and that in turn leads to a clot.
Tator said that when blood collects or clots inside the skull, pressure builds up and pushes the brain downward. Unless this aggregation of blood is removed and the pressure released through surgery, the brain stem can become compressed.
"And that's when the serious, generally irreversible damage occurs," Tator said. "So if there has been damage to the brain stem, those people generally don't wake up. They either die or remain in a vegetative state."
The shame of it is that traumatic brain injuries from spills during skiing and other sports can often be prevented by the use of a helmet, said Tator, founder of ThinkFirst, a national non-profit organization aimed at preventing brain and spinal cord injuries.
Richardson was reportedly not wearing a helmet when she fell during private lessons with an experienced instructor at the tony Quebec resort.
"Wearing a helmet does make a big difference," Tator said. "We really are preaching helmets now for virtually all winter sports."
Neeson immediately left the Toronto set of his upcoming movie, "Chloe," for Montreal, a publicist for the film said.
Richardson's films include "Gothic," "A Month in the Country," "Nell" (in which she appeared with her future husband), "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 in 1998 for playing Sally Bowles in a revival of "Cabaret."
Her maternal grandparents were the actors Michael Redgrave and Rachel Kempson, and her uncle Corin and aunt Lynn Redgrave are both actors. Sister Joely Richardson is also an actress, best known for starring in the TV series "Nip/Tuck."
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 Studio 54 in New York.
She married Neeson in 1994, and the couple have two sons, aged 13 and 12.