"It’s being reported that certain key Democratic polling locations in Clark County were kept open for hours and hours beyond closing time to bus and bring Democratic voters in," Trump said.
"Folks, it's a rigged system. It's a rigged system. And we're going to beat it," he said.
"Last night in Clark County they kept a poll open until 10 o'clock at night so a certain group could vote. It wasn't in an area that normally has high transition," he said. "You think this is a free and easy election?"
Clark County, according to the latest census data, is over 30 percent Hispanic. Data show Democrats outregister Republicans.
According to ABC station KNTV, more than 57,000 people voted in Clark County on Friday as of 10 p.m., breaking a record for single-day early voting.
Clark County has cited no evidence of any wrongdoing.