Tuesday is election day in America, marking the end of a fractious presidential campaign between president Donald Trump and former vice president Joe Biden that has exposed the deep divides across the country.

More than 100m votes have already been cast as mass early voting was driven by concerns about crowded polling stations during the coronavirus pandemic as well as extraordinary enthusiasm.

Biden appeared to be leading, according to national opinion polls, and Barack Obama’s former second-in-command also seems to be ahead in the key “battleground” states. It is swing states including Florida, North Carolina and Pennsylvania that will decide who wins thanks to the Electoral College system.

Both candidates are striving for the magic number of 270 Electoral College votes, but it could take a long time before the result is known as some key swing states do not begin counting mail-in ballots until election day. Polls show that postal voters are disproportionately likely to support Biden, which on election night could lead to a “red mirage”, where Trump takes an initial lead until absentee ballots are counted over the course of days.