One of the sources said Manson was seriously ill but could not provide specific information.
The sources requested anonymity because they were not authorized to speak publicly about the matter.
Officials with the California Department of Corrections and Rehabilitation declined to comment, citing federal and state laws and saying inmates' medical information is private.
"We do not disclose inmate movements for safety and security reasons," said Terry Thornton, a department spokeswoman.
However, she said: "He is alive."
On Wednesday, a San Joaquin Community Hospital of Bakersfield spokeswoman told The Times that Manson was not a patient at the facility or receiving treatment in any way. The hospital is one of two in the area that treats patients from Corcoran state prison.
At least one source, who was not authorized to discuss the matter, said Manson was admitted to Mercy Hospital earlier this week. Officials at Mercy Hospital in downtown Bakersfield have refused to comment. The hospital regularly treats patients from the state prison, and its emergency room is where many inmates end up when sudden life-threatening illness or injuries occur.
Manson and other members of his so-called family were convicted of killing actress Sharon Tate and six other people during a bloody rampage in the Los Angeles area during two August nights in 1969. Prosecutors said that Manson and his followers were trying to incite a race war that he believed was in the Beatles' song "Helter Skelter."
Tate, the wife of director Roman Polanski, was 8½ months pregnant when she was killed at her hilltop home in Benedict Canyon on Aug. 9, 1969. Besides Tate, four others were stabbed and shot to death: Jay Sebring, 35; Voytek Frykowski, 32; Abigail Folger, 25, a coffee heiress; and Steven Parent, 18, a friend of Tate's caretaker. The word "Pig" was written on the front door in blood. The next night, Manson rode along with his followers to the Los Feliz home of Leno and Rosemary LaBianca, then left three members to kill the couple.
Manson, now 82, has had "hundreds" of rules violations, prison officials say, and has been in trouble for having a cellphone and a homemade weapon while incarcerated. Manson has been denied parole 12 times. His next parole hearing is scheduled for 2027, when he will be 92. He has been in prison since 1971 and is serving his time at Corcoran State Prison.
In 2014, Manson and Afton Elaine Burton, a 26-year-old Manson devotee, were granted a marriage license, but it expired before the two could marry.
Last week, state parole officials postponed a decision on granting parole to Patricia Krenwinkel, a Manson follower and convicted killer, after her attorney made new claims that she had been abused by Manson or another person.
Krenwinkel was sent to death row in 1971 after a Los Angeles jury convicted her in the Tate murders.
Several Bakersfield media outlets said a corrections department van was parked outside Bakersfield's Mercy Hospital. The Bakersfield Californian reported Manson was admitted there Sunday under a "Joe Doe" name. The paper said Manson was not in the intensive care unit.
12:00 p.m.: This article was updated with comments from hospital officials.
7:43 a.m., Jan. 4: This article was updated with information about Manson follower Patricia Krenwinkel's parole hearing and a report that Manson was not in intensive care.
7:40 p.m.: Updated with more information about the hospital where Manson is being treating.
4:40 p.m.: This post was updated with more background.