The zoo and the China Conservation and Research Center for the Giant Panda "have the great pleasure to announce the birth of a panda cub", Pairi Daiza said in a statement.
"Less than 2,000 pandas can be found in the wild, making every birth a true miracle", it said.
"Over the past twenty years, only two European countries (Austria and Spain) were able, with China's help, to successfully reproduce pandas.
"Belgium will thus be the third European country to have ever had the pleasure of welcoming a panda cub."
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She was artificially inseminated twice in February with the sperm of Xing Hui.
The zoo, in Brugelette, about 50 kilometres west of Brussels, said last month that Hao Hao was showing signs she could be pregnant, but had remained cautious over whether she would actually give birth.
"For several weeks, she ate twice the usual amounts of bamboo, then she became increasingly disinterested in food and began to refuse to leave her cave", Hao Hao's minder Tania Stroobant had said.
There remain about 1,800 freely roaming pandas in the world, with about 400 in captivity, mainly in southwest China.