Alleged South Carolina serial killer Todd Kohlhepp has been charged with three more murders, bringing the total to seven, police said.

Kohlhepp, 45, was arrested early in November when police investigating a sex crimes allegation found missing Kala Brown, 30, chained in a metal container in his property in Woodfruff.

The body of her boyfriend, Charles Carver was found in a shallow grave on Kohlhepp's property. Brown said she saw Kohlhepp shoot Carver.

Kohlhepp then led investigators to the grave sites of Meagan Coxie, 25, and Johnny Coxie, 29, authorities said.

Police believe he shot Meagan Coxie on Christmas Day or December 26 last year, and shot Johnny Coxie about a week previously.

He is alleged to have shot Carver between 30 August and 2 September.

He has been charged with murdering Carver and the Coxies, and has also been charged with multiple weapons and kidnapping offences in relation to their deaths, Associated Press reported.

Kohlhepp was being held without bond at Spartanburg County jail after confessing after his arrest to four other murders committed near the town of Chesnee in 2003, said Sheriff Chuck Wright.