By Toni Guinyard, Jonathan Lloyd and Melissa Pamer, NBC News

With a record number of registered voters in Los Angeles County, election officials expected significant turnout as voters headed to the polls Tuesday to cast ballots in a hotly contested presidential race and myriad statewide and local contests.

Polls opened across the state at 7 a.m. and will remain open till 8 p.m. Registrar-Recorder/County Clerk Dean Logan tweeted as polls closed on the East Coast: “Don’t let east coast results & predictions keep you from voting in L.A. — every vote counts. Polls open until 8 PM.”

At 4 p.m., voter turnout was at 46 percent in LA County.

Results in close contests could be delayed because of a high number of mail-in ballots that remain to be counted, Los Angeles County Registrar-Recorder/County Clerk officials cautioned.

Voters can cast ballots or submit a mail-in ballot at their polling place. More than 9 million mail-in ballots were issued in California.

About 26,000 polling place volunteers were preparing for voters early Tuesday at the Cypress Park Recreation Center and more than 4,600 other locations in LA County.

LA county has 4.7 million registered voters — a 10 percent increase since 2008 — and a record high. The county accounts for nearly a quarter of California’s 18.2 million registered voters.

About 1.5 million vote-by-mail ballots were issued in LA County, and Registrar-Recorder/County Clerk Dean Logan said some of those forms won’t be ready to be counted till Friday.

“If we have close contests or measures hanging in the balance tonight, it could be days and even weeks before we see the vote totals on that,” Logan said.

Voter registration has been “phenomenal” with the introduction of online registration in September, Logan said. Many of the online registrants were between ages 18 and 29, Logan said.

Whether that will translate to a high turnout will be determined Tuesday night.

“Voter registration is certainly that intent to participate,” Logan said. “But on Election Day, we see the culmination in all that intent and the energy of people doing the physical  act of marking their ballot.”

Early morning and late afternoon are traditionally the busiest times at the polls, Logan said. He suggested voting at mid-day, if possible.

For last-minute voters, Logan said anyone in line at the time polls close will be allowed to cast a ballot.

All ballots will be transported to the county registrar’s office in Norwalk in an LA County Sheriff’s patrol vehicle. The final returns are likely to come from Santa Catalina Island, Logan said.