Voters in six states -- California, Montana, New Jersey, New Mexico, North Dakota and South Dakota -- are casting their ballots in the Democratic or Republican races for president. North Dakota is holding Democratic caucuses only.

Donald Trump has clinched the GOP nomination already, and Hillary Clinton secured the Democratic nomination on Monday.

Here's a guide to each race, with live updating vote results:

Republican races

Polls closing at 8 p.m. ET: New Jersey

Polls closing at 9 p.m. ET: New Mexico, South Dakota

Polls closing at 11 p.m. ET: California

Democratic races

Polls closing at 8 p.m. ET: New Jersey

Polls closing at 9 p.m. ET: New Mexico, South Dakota

9 p.m. caucus: North Dakota (Democratic only)

Polls closing at 11 p.m. ET: California