Well-known TV anchor Ces Drilon is among those who remain hostage
A TV cameraman has been freed by kidnappers in the southern Philippines, but two fellow journalists from the ABS-CBN network remain captive.
Angelo Valderama was freed late on Thursday and immediately flown off the troubled island of Jolo.
But presenter Ces Drilon and cameraman Jimmy Encarnacion are still being held, along with academic Octavio Dinampo.
Authorities say they suspect the militant Islamist group Abu Sayyaf of being behind the kidnappings.
The group is notorious for using bombings, kidnappings and other violence in its separatist campaign, and has beheaded kidnap victims in the past.
In a separate development, rebels freed two Philippine marines captured on Tuesday on the nearby island of Basilan, officials said.
Ms Drilon and her crew, who all work for ABS-CBN - the Philippines' largest TV network - were seized in a Jolo township on Sunday.
Mr Valderama's release was negotiated by a team including Isnaji Alvarez, mayor of the Jolo township of Indanan.
His release has been welcomed by the families of the remaining captives, who released a statement urging the kidnappers to release them as "an act of compassion and humanity".
Hainatul Dinampo, wife of the kidnapped academic, appealed for help sending medication to her husband, who suffers from arthritis and high blood pressure, AFP news agency reported.
But Mr Alvarez later said negotiators had not been able to reach the kidnappers, who appeared to have switched their mobile phones off, AFP said.
The captors are said to be demanding a ransom of at least 10 million pesos ($225,000) for the hostages.
Mr Alvarez confirmed that a "minimal" sum of money had been given to the kidnappers for "board and lodging" expenses.
But it is unclear whether any sizeable ransom has been paid.
Both the government and ABS-CBN say they do not pay ransoms as they could provide an incentive for further kidnappings.