Election officials said there were long lines at some polling places early on, but shorter waiting times in the afternoon. No major problems were reported.
Secretary of State Ross Miller has said he expects a record turnout in the Nov. 4 election because of high interest in the presidential election.
He urged the state's nearly 1.5 million registered voters to take advantage of early voting at grocery stores, libraries, government buildings and shopping malls through Oct. 31.
"We had over 8,000 votes cast as of noon," said Larry Lomax, voter registrar in Clark County around Las Vegas. "It's always busy when it first opens. The lines are nothing unreasonable."
That was not the case at the downtown Reno library, where it took nearly an hour for some voters to cast a ballot Saturday morning, Washoe County Voter Registrar Dan Burk said.
"That's what happens when you have several hundred people waiting in line," he said. "Apparently, some organizations had dropped off people there."
Burk said waits of 35 or 45 minutes were reported at most locations early on, but they were down to about 15 minutes in the afternoon. More than 3,000 ballots had been cast in Washoe as of 1 p.m.
Early voting is expected to account for about half of the total vote in Clark County and 30 percent of it in Washoe County.
Lomax and Burk said they expect a voter turnout of 75 percent to 80 percent because the state is a critical battleground in the presidential election.
"That's what's bringing people out," Burk said. "If people ever thought about wanting their vote to make a difference, this is their opportunity."
One recent poll found Democratic presidential candidateand Republican presidential contender in a statistical tie in Nevada, while another found Obama with a slight lead.
Figures released by the secretary of state's office on Friday show Nevada Democrats have increased their voter registration edge over Republicans to more than 110,000 - far above their slight edge of about 4,100 voters only a year ago.
The big gain for Democrats reversed about a 4,400-voter edge that Republicans had in the 2004 elections.
President Bush narrowly carried Nevada in 2004 and 2000.