April Fools is no laughing matter, China's official news service intoned Friday, saying the Western tradition of opening spring with a gag is un-Chinese.
The official news agency Xinhua's stiffly worded post on micro-blog Weibo declared: "Today is the West's so-called 'April Fools'".
The occasion "does not conform with our nation's cultural traditions, nor does it conform with the core values of socialism", it added.
"Don't believe rumours, don't create rumours and don't spread rumours," it said, capping off the note with a smiley emoticon.
A cartoon accompanying the post showed two phones "spreading rumours." A finger pointing at them is accompanied by a word bubble that says "breaking the law".
Spreading rumours online can be a violation of Chinese law.
But the country's Internet users met the reminder with a collective guffaw, suggesting that in China, every day is April Fools.
"You speak lies every day, use government policy, data, to trick the people in every way. What's up, what's down? What's wrong? What's right? We're on to you," one Weibo commenter said.
Other users likened the post to the satirical American newspaper The Onion.
"The most amusing 'April Fools' news is that Xinhua is seriously saying 'don't believe rumours'," said one.
Even the Global Times, a paper closely tied to the ruling Communist Party, seemed to suggest Xinhua needed to loosen up.
"How many friends have you fooled today?" it asked on Twitter -- which is not accessible in China. "Here are some pranks for #Aprilfools."
But Xinhua did not see the funny side.
There were 36 replies to its original Weibo post, none of which was visible after comments were blocked.