US President Donald Trump and his Democratic rival Joe Biden are holding competing prime-time Q&A sessions.
The events replace a cancelled second presidential debate after Mr Trump’s refusal to participate virtually following his Covid-19 diagnosis.
Both candidates are fielding questions from voters – Mr Trump in Miami and Mr Biden in Philadelphia.
The events are being broadcast on rival US networks.
Millions of early ballots have already been cast for the 3 November election.
Opinion polls suggest Mr Biden has a 10-point advantage over Mr Trump nationally, but his lead in some key states is narrower.
Campaigning has picked up the pace this week, with Mr Trump holding rallies in the battleground states of Florida, Pennsylvania and Iowa, and Mr Biden travelling to Ohio and Florida.
What do we know about the events?
Thursday should have been the candidates’ second debate ahead of the 3 November election. But the committee organising the debates said it wanted to “protect the health and safety of all involved” by changing the format to a virtual debate after Mr Trump tested positive for coronavirus. The president then refused to appear virtually rather than in person so the event was cancelled.