Philippine Nobel Peace Prize winner Maria Ressa lost her appeal against a conviction for cyber libel, her news website Rappler said Friday, in the latest blow for the veteran journalist.

Ressa, 58, and her former colleague Rey Santos Jr face lengthy jail sentences, but the company said they will "avail of all legal remedies available to them", including taking the case to the Supreme Court.

The ruling comes less than two weeks after Philippine authorities ordered Rappler to shut down ahead of outgoing president Rodrigo Duterte's last day in office.

Rappler on Friday described the decision to uphold the 2020 conviction as "unfortunate", saying it "weakens the ability of journalists to hold power to account".

"What is ultimately at stake is our democracy whose strength rests on a media that is not threatened by the state nor intimidated by forces out to silence critical voices," Rappler said.

Ressa, who is currently in Manila, has long been a vocal critic of Duterte and the deadly drug war he launched in 2016, triggering what media advocates say is a grinding series of criminal charges, probes and online attacks against her and Rappler.

She and Russian journalist Dmitry Muratov were awarded the Nobel Peace Prize in October for their efforts to "safeguard freedom of expression".

In a statement on Friday, Norwegian Nobel Committee chair Berit Reiss-Andersen said: "The criticism voiced through Rappler is well within the freedom of expression in a democratic society. I am gravely concerned that Maria Ressa is being prosecuted for exercising her rights of expression."

Ressa, who is also a US citizen, is fighting at least seven court cases, including the cyber libel case, for which she has been on bail and faces up to nearly seven years in prison.

Rappler, which faces eight cases, had to fight for survival as Duterte's government accused it of violating a constitutional ban on foreign ownership in securing funding, as well as tax evasion.

The cyber libel law was introduced in 2012, the same year Rappler was founded.

Its use against journalists was "troubling", said Jonathan de Santos, chairman of the National Union of Journalists of the Philippines.

Philippines' Nobel Peace Prize winner Maria Ressa lost her appeal against a conviction for cyber libel
Philippines' Nobel Peace Prize winner Maria Ressa lost her appeal against a conviction for cyber libel AFP / Odd ANDERSEN

He called on Congress to descriminalise cyber libel, arguing it was "no longer compatible with our constitution".

Just days before Duterte left office, the Philippine Securities and Exchange Commission (PSEC) ordered Rappler to shut down for violating "constitutional and statutory restrictions on foreign ownership in mass media".

The news organisation is accused of allowing foreigners to take control of its website through its parent company Rappler Holdings' issuance of "depositary receipts".

Under the constitution, investment in media is reserved for Filipinos or Filipino-controlled entities.

Rappler said the PSEC's decision "effectively confirmed the shutdown" of the company and vowed to appeal, describing the proceedings as "highly irregular".

Ressa said the company would continue to operate as they followed the legal process, but expressed hope that the situation would improve under Duterte's successor, Ferdinand Marcos Jr.

But the company's future and its battle in the country's highly politicised legal system under Marcos Jr's presidency is uncertain.

Marcos Jr, who took over from Duterte on June 30, has given few clues about his views on the website and the broader issue of freedom of speech.

But activists fear he could worsen the situation for human rights and freedom of speech in the country.