US midterms: Nevada may decide control of Senate after Democrats win in Arizona

Control of the US Senate may come down to Nevada, where a slow ballot count entered its final act on Saturday.

In a nail-biting contest, Democratic Senator Catherine Cortez Masto is squaring off against Republican challenger Adam Laxalt.

Saturday is the last day that mail ballots can arrive and be counted under the state's new voting law.

Election officials were hustling to get through a backlog of tens of thousands of ballots to determine the race's winner.

The Nevada race took on added importance after Democratic Senator Mark Kelly was declared the winner of his re-election campaign in Arizona, on Friday night, giving his party 49 seats in the chamber - the Republicans also have 49.

If Ms Cortez Masto wins, Democrats would maintain their control of the Senate given Vice President Kamala Harris' tiebreaking vote.

However, should Mr Laxalt win, then the Georgia Senate runoff next month would determine which party has the single-vote Senate edge.

Ms Cortez Masto was only a few hundred votes behind Mr Laxalt, with most of the remaining uncounted ballots in heavily Democratic Clark County, which includes Las Vegas.

Mr Laxalt said he expects to maintain his advantage and be declared the victor.

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But on Saturday he acknowledged in a tweet that the calculus has changed because his rival had performed better than Republicans expected, in Clark County ballots counted over the past few days.

"This has narrowed our victory window," he tweeted, acknowledging the race comes down to the final Clark ballots.

"If they are GOP precincts or slightly DEM leaning then we can still win," Laxalt tweeted. "If they continue to trend heavy DEM then she will overtake us."

In the scenario that the race remains too close to call after Saturday, a few thousand more ballots could be added to the totals early next week.

Mail ballots with clerical errors can be "cured" by voters until the end of Monday, and then added to the totals.

"We are doing everything in our power to move ballots forward just as quickly as we can," Joe Gloria, the registrar in Clark County, said.

An estimated 23,000 ballots remain to be counted in the county. Mr Gloria said there were also 9,600 ballots being "cured" and 5,555 provisional ballots.

Meanwhile, in another key race, Democratic Governor Steve Sisolak lost his re-election bid to his Republican challenger, sheriff Joe Lombardo, on Friday.