The former US president spoke on Show Me Your Walk, HBCU Edition, a two-hour event for students graduating from historically black colleges and universities broadcast on YouTube, Facebook and Twitter. His remarks were unexpectedly political, given the venue, and touched on current events beyond the virus and its social and economic impacts.

"More than anything, this pandemic has fully, finally torn back the curtain on the idea that so many of the folks in charge know what they're doing," Obama said. "A lot them aren't even pretending to be in charge."

Later on Saturday, during a second televised commencement address for high school seniors, Obama panned "so-called grown-ups, including some with fancy titles and important jobs" who do "what feels good, what's convenient, what's easy".

"Which is why things are so screwed up," he said.

Obama did not name President Donald Trump or any other federal or state officials in either of his appearances. But earlier this month, he harshly criticised Trump's handling of the pandemic as an "absolute chaotic disaster" in a call with 3000 members of his administrations obtained by Yahoo News.

The commencement remarks were the latest sign that Obama intends to play an increasingly active role in the coming election. He has generally kept a low profile in the years since he left office, even as Trump has disparaged him. Obama told supporters on the call that he would be "spending as much time as necessary and campaigning as hard as I can" for Joe Biden, who served as his vice president.

As he congratulated the college graduates and commiserated over the enormous challenges they face given the devastation and economic turmoil the virus has wrought, the former president noted the February shooting death of Ahmaud Arbery, 25, who was killed while jogging on a residential street in Georgia.

"Let's be honest: A disease like this just spotlights the underlying inequalities and extra burdens that black communities have historically had to deal with in this country," Obama said.

"We see it in the disproportionate impact of COVID-19 on our communities, just as we see it when a black man goes for a jog and some folks feel like they can stop and question and shoot him if he doesn't submit to their questioning."

"Injustice like this isn't new," Obama went on to say. "What is new is that so much of your generation has woken up to the fact that the status quo needs fixing, that the old ways of doing things don't work." In the face of a void in leadership, he said, it would be up to the graduates to shape the future.

"If the world's going to get better, it's going to be up to you," he said.

Australian Associated Press