French President Francois Hollande held an emergency ministerial meeting on Friday morning to discuss the impact the Brexit vote from the UK on Thursday.
"The British vote poses a grave test for Europe, which must show solidity and strength in its response to the economic and financial risks," Hollande said.
He added that the vote was "a painful choice that he already regrets", and that France would continue to work with the UK, which he called a "great ally", reported the BFM TV channel.
Friday's historic vote sent tremors across the English Channel, where the rest of the political class had mixed reactions to the news.
French far-right leader Marine Le Pen was - as perhaps could have been expected given the result - the quickest off the blocks to react to the referendum result in the UK.
The far-right national front leader hailed Britain's decision to leave the European Union and called for a similar referendum in France.
"Victory for Freedom! As I have been asking for years we must now have the same referendum in France and EU countries," the National Front (FN) leader tweeted.
Fears are high that a domino effect could see other countries following in Britain's footsteps, threatening the core of the European project.
Paris Mayor Anne Hidalgo described it as a "sad day for Europe".
The mayor however vowed to continue building links between the UK and France.