One of his close friends, Tenky Tin Kai-man, said Ng died at 5.16pm in Union Hospital, according to The Standard of Hong Kong.
Family members of Ng, including his wife, children and siblings, were at his death bed.
"He left us peacefully. Doctors had been prescribing medications to make his feel better, he passed away in his sleep," Tin said.
But Tin refused to describe mental conditions of Ng's family members, saying no one would wish to see their beloved ones pass away.
Ng, who started his career at the age of 22 in 1973, was known for his roles in movies with comedian Stephen Chow Sing-chi, including "The Final Combat", "The Justice of Life" and “Shaolin Soccer."
In 1991, the late actor was awarded Hong Kong Film Award's Best Supporting Actor for his role in "A Moment of Romance," featuring prominent star Andy Lau Tak-wah.
Ng also received several nominations for his acting, including the Hong Kong Film Awards and Taiwan's Golden Horse Awards.
Ng had been struggling with deteriorating health conditions in recent years. In 2014, he was rushed to a hospital due to breathing problems, and was later diagnosed with a heart failure.
The news was also confirmed by his close friend Tin Kai Man, who revealed that Man Tat passed away peacefully in his sleep at 5.16pm today (Feb 27) at the Union Hospital in Hongkong, as reported by Today Online.
Kai Man told the media, “Doctors prescribed medicine to make him feel better and he passed away peacefully (...) with his wife, children and siblings by his side.”
The actor was reported to have had surgery recently after being diagnosed with liver cancer, and was also undergoing chemotherapy.
Kai Man previously shared with the media that Man Tat was “weak” from chemotherapy and that he could only communicate with others using hand gestures.
Man Tat’s health has been deteriorating in recent years.
In 2014, he was warded in the intensive care unit due to heart failure from a viral infection.
Just last month, he is believed to have suffered a heart attack after a video of him clutching his chest in pain while on the set of a shoot went viral.