He also wrote lengthy posts on Medium and Instagram about the recent wave of protests against police brutality, and with a similar call to action.

The coronavirus pandemic "just brought into focus problems that have been growing for a very long time," Obama said on Sunday, citing economic inequality, lack of basic health care, bigotry and political polarisation.

Recent protests "speak to decades worth of anguish and frustration over unequal treatment and a failure to reform police practices and the broader criminal justice system," Obama said.

Aspirations for change have to be translated into laws and institutional practices at every level of government, including those "that don't get as much attention as a presidential race," he said.

Obama also spent a large part of his speech warning about the perils of relying on social media for information, urging "the internet generation" to "listen to each other, respect each other, and use all that critical thinking you've developed from your education to help promote the truth".

"Too often [social media] shut us off from each other instead of bringing us together - partly because it gives us the ability to select our own realities, independent of facts or science or logic or common sense. We start reading only news and opinions that reinforce our own biases and start cancelling everything else out; we let opinion masquerade as fact and treat even the wildest conspiracy theories as worthy of consideration."

"Tt's going to be up to you to create online cultures and communities that respect differences of opinion and freedom of speech, and also restore the kind of honest, informed and fact-based debate that is the starting point for tackling the challenges we face."

Michelle Obama struck a similar tone at the virtual graduation, which featured A-list artists such as Beyonce, Taylor Swift, Lady Gaga and K-pop group BTS.

"If you're spending a lot of time just hashtagging and posting right now, that's useful, especially during a pandemic," the former first lady said. "But it's only a beginning. Go further. Send all your friends a link to register to vote."

-Bloomberg