Polling places close in Mississippi at 8 p.m. Eastern.
Elsewhere in the United States, there were equipment-related delays reported in select counties in Ohio, Texas and Georgia.
The Federal Bureau of Investigation (FBI) said it was also investigating robocalls in Michigan and Iowa reportedly telling voters to “stay home and stay safe” rather than turn out to vote.
Nearly 102 million Americans cast ballots ahead of Election Day.
U.S. President Donald Trump has already threatened legal action to prevent the counting of ballots that arrive after Election Day, which some states allow. Meanwhile, a federal judge ordered postal workers in some major cities to sweep processing facilities for any remaining ballots before the end of the day.
Collection and processing of ballots by mail had earlier been curtailed by orders of the Postmaster General, Louis DeJoy, who happens to be a major Republican Party donor.
--With files from the Associated Press