WASHINGTON, Oct. 22 (Xinhua) -- The second and final round of U.S. presidential debate between incumbent Donald Trump and Democratic nominee Joe Biden kicked off Thursday night, offering voters the last chance before Election Day to see the candidates facing each other head-on and making their cases for the presidency.

Held at Belmont University in Nashville, Tennessee, the debate, which runs for an uninterrupted period of 90 minutes, will feature six topics chosen by NBC News' White House correspondent Kristen Welker, who moderates the event. They are "Fighting COVID-19," "American Families," "Race in America," "Climate Change," "National Security" and "Leadership."

The candidates, neither of whom wore masks while speaking, stood behind their respective podiums with no plexiglass erected in front of them, an arrangement made after their campaigns consulted with Anthony Fauci, the country's leading infectious disease expert and a member of the White House Coronavirus Task Force. Both candidates tested negative for the virus before stepping onto the stage.

Thursday's face-off should have been the third debate, but Trump declined to participate in the session originally scheduled for Oct. 15 after it was altered to a virtual format due to the president's COVID-19 diagnosis, resulting in both teams holding their own town hall meetings with voters that day.

To avoid the chaos of mutual interruption that defined the pair's first encounter on Sept. 29, the Commission on Presidential Debates, the nonpartisan organizing body of the event, made a change to the rules that will mute the candidates' microphones when their opponents are given two minutes to answer the first question of each of the six 15-minute segments, so that the one who is speaking will not be interrupted.

While Trump is still lagging behind Biden in national and battleground state polls, the Biden campaign has recently warned against complacency, arguing that races in several critical swing states are actually far closer than what the polls suggest.