Press freedom has never been as threatened as it is now, in the "new post-truth era of fake news", strongmen and propaganda, Reporters Without Borders said.
Its annual World Press Freedom Index, published on Wednesday, warned of a "tipping point" for journalism.
"Attacks on the media have become commonplace and strongmen are on the rise. We have reached the age of post-truth, propaganda, and suppression of freedoms - especially in democracies," the report said.
"Media freedom has never been so threatened."
Syria, where a bloody civil war has entered its sixth year, was the deadliest country for journalists, according to the watchdog, known by its French initials RSF.
Recep Tayyip Erdogan's Turkey, which has jailed 81 journalists after a failed coup attempt, and Abdel Fattah el-Sisi's Egypt, where Al Jazeera's Mahmoud Hussein has been detained, were branded the world's biggest prisons for journalists.
Hussein is awaiting trial on charges of spreading false news, a charge Al Jazeera denies.
Also in several democracies, "nothing seems to be checking" the erosion of liberty of the press, RSF said.
It blamed the continuing fall to "an obsession with surveillance and violations of the right to confidentiality of sources".
These include the US and Britain, which both slipped two places in the index to 43rd and 40th.
The report also warned of the "highly toxic" media-bashing of US President Donald Trump's election campaign and Britain's Brexit referendum, saying this has pushed "the world into a new era of post-truth, disinformation and fake news."
RSF Secretary General Christophe Deloire said: "The rate at which democracies are approaching the tipping point is alarming for all those who understand that, if media freedom is not secure, then none of the other freedoms can be guaranteed."
"Where will this downward spiral take us?" he asked.
In the past year nearly two thirds of the countries had registered a deterioration in their situation, while the number of countries where the media freedom situation was "good" or "fairly good" fell by more than two percent, the report found.
"Media freedom has retreated wherever the authoritarian strongman model has triumphed," the report went on.
Turkey "swung over into the authoritarian regime camp" after the failed coup against President Erdogan in July, it said, adding that it "now distinguishes itself as the world's biggest prison for media professionals".
Seven places ahead of Turkey, "Vladimir Putin's Russia remains firmly entrenched in the bottom fifth of the index," in 148th place, it added.
Liberty of the press is in peril or in a "very serious situation" in 72 countries, including Russia, India and China, the report found.
Norway came out top of the index with the world's freest media.
North Korea took bottom place from another repressive closed state, Eritrea, which has propped up the table for a decade.
North Korea continues to keep "its population in ignorance and terror," RSF said. "Even listening to a foreign radio broadcast can lead to a spell in a concentration camp."
Source: Al Jazeera and news agencies