"Delete your account."

Hillary Clinton's snarky tweet Thursday to her White House rival Donald Trump was among the funniest of the campaign. Almost as funny as it was awkward.

The message by the 68-year-old former secretary of state -- actually written by a young staffer, a Clinton aide told AFP -- was in response to the latest broadside by Trump, who had commented on how "Obama just endorsed Crooked Hillary" on Thursday.

"He wants four more years of Obama — but nobody else does!" the presumptive Republican nominee added.

When Clinton trolled back, social media exploded.

Within two hours her message was retweeted 200,000 times, making it "the most retweeted tweet of the campaign!" according to Clinton's social media director Alex Wall.

With "Delete your account," Clinton, who has struggled to connect with young voters, embraced the quick-witted dry humor of America's millennials.

But it also triggered ferocious comebacks from her critics over use of a private email account while she served as America's top diplomat -- a scandal she has been unable to shake.

Republicans including Trump have savaged her for her judgment, saying she put US national security at risk, and have accused her of deleting key emails that she did not want Americans to see.

"@HillaryClinton, If anyone knows how to use a delete key, it's you," the chairman of the Republican National Committee, Reince Priebus, wrote in a stinging tweet of his own.

Trump, known for his sharp tongue on social media, returned fire against Clinton, mocking her less-than-spontaneous attempt at hipness.

"How long did it take your staff of 823 people to think that up -- and where are your 33,000 emails that you deleted?" he wrote.

Clinton turned over some 30,000 emails to State Department officials after she stepped down from the job in 2013.

But she also said she deleted more than 30,000 other emails that were of a personal nature and not related to her work as secretary of state.