RTBF reporters kept up the spoof for nearly two hours
Belgians reacted with widespread alarm to news that their country had been split in two - before finding out they had been spoofed.
The Belgian public television station RTBF ran a bogus report saying the Dutch-speaking half of the nation had declared independence.
Later it said Wednesday night's programme was meant to stir up debate.
It appears to have succeeded. Thousands of people made panicked calls to the station and politicians complained.
"It's very bad Orson Welles, in very poor taste," said a spokesman for Prime Minister Guy Verhofstadt, referring to the famous director's 1938 radio adaptation of War of the Worlds. That spoof fooled many Americans into believing Martians had invaded.
We obviously scared many people - maybe more than we expected
RTBF head of news
"In the current context, it's irresponsible for a public television channel to announce the end of Belgium as a reality presented by genuine journalists," he added.
The French-language TV channel interrupted regular programming with an apparent news report, announcing that Dutch-speaking Flanders had unilaterally declared independence and that Belgium as a nation had ceased to exist.
It showed "live" pictures of cheering crowds holding the Flemish flag, huge traffic jams leading to Brussels airport, and trams stuck at the new "border".
RTBF showed shots of flag-waving independence supporters
The broadcast came amid an apparent growth of separatist sentiment in Flanders.
Recent regional elections have shown strong support for the far-right, nationalist Vlaams Belang party, which advocates Flemish independence.
The station's website crashed briefly as alarmed viewers sought more information, and 2,600 calls were made to a telephone number given out during the spoof.
"Our intention was to show Belgian viewers the intensity of the issue of the future of Belgium and the real possibility of Belgium no longer being a country in a few months," Yves Thiran, head of news at RTBF, told the BBC.
He said it introduced people to the debate who would otherwise have ignored it, but he admitted some may have taken it the wrong way.
"We obviously scared many people - maybe more than we expected," he said.
Some politicians were in on the joke, contributing interviews to the programme with their reactions to the "news". But others were not amused.
The minister for audiovisual affairs for the French-speaking community, Fadila Laanan, said the words "this is fiction" appeared on screen half an hour into the broadcast - at her insistence.
"I find it questionable to use such a tactic, which frightened people unbelievably," she said, adding that a number of people had called her in panic when the "news" broke.
The AFP news agency reported that even some foreign ambassadors in Brussels were taken in, and sent urgent messages back to their respective capitals.