The 45-year-old was involved in an accident on the slopes in Quebec, Canada on Monday and was taken to Montreal's Centre Hospitalier Laurentien, before being transferred to the nearby Hopital du Sacre-Coeur de Montreal.
Richardson is under constant supervision from medics after suffering a "traumatic brain injury", a hospital source told IrishCentral.com.
And a representative for Neeson's forthcoming movie Chloe, which he had been filming in Toronto at the time of the incident, has confirmed the Irish actor has left the set to be at his wife's bedside.
The spokesperson tells Canada Television, “Liam Neeson left the Toronto set immediately to fly to Montreal upon news of his wife’s accident. We do not have any details at this time but we hope for the best and our thoughts and prayers are with Natasha and Liam and their family.”
Richardson's uncle, Corin Redgrave, brother of her actress mother Vanessa Redgrave, says, "I have heard this morning from a family representative about Natasha's accident and am very saddened.
"We are very much thinking of Natasha, Vanessa and (sister) Joely, and are sending them our love."
No further information was available as WENN went to press.