A race to be governor of a US state often receives less international attention than a congressional contest, but with 36 governor's mansions up for grabs in Tuesday's midterm elections the state governance of hundreds of millions of people is at stake.

Governors wield considerably more power than most senators or congressmen, with the executive clout to do everything from expand healthcare provision to oversee electoral redistricting.

Twenty-six of the contested mansions are currently held by Republicans, nine by Democrats and one by an independent. 

Nine of 10 largest states in the US will vote for a new governor on Tuesday, and FiveThirtyEight forecasts that post-election Democrats will govern 62.6 percent of the US population to the Republicans' 37.4 percent at a state level.

Here's a rundown of five high profile, toss-up races to watch as the results roll in. 

- Republican Scott Walker, the incumbent governor, has won three-statewide races in Wisconsin but the 51-year-old has trailed in most polls over the past month. 

- Democrat Tony Evers appears in pole position to win the governor's mansion, but the 66-year-old public official and former teacher will be wary of the advantages of incumbency.  

- 2016: Trump 47.22 percent, Clinton 46.45 percent

Why it matters:

The Democrats are desperate to depose Walker in a state that was narrowly lost to Donald Trump in the 2016 presidential election. Two-term governor Walker is a Republican favorite who briefly entered the race for the White House two years ago, and a nemesis for Democrats given his staunch conservatism and anti-union policies. He would be a major scalp for the Democrats. 

- Republican Ron DeSantis is the underdog according to the latest polling, but a 2.6-point average polling deficit puts the 40-year-old congressman within the margin of error. 

- Democrat Andrew Gillum, the mayor of Tallahassee, has consistently held a narrow lead in the polls and was boosted on Friday when former president Barack Obama joined him on the stump. 

- 2016: Trump 48.6 percent, Clinton 47.4 percent

Why it matters:

The high profile Florida race pits a Republican who has modeled himself on Donald Trump against a Democrat firmly on the progressive wing of the party. DeSanctis went so far as to release an ad in which he told his children to say 'Make America Great Again' while Gillum has called for the replacement of the Immigration and Customs Enforcement agency. The sometimes ugly contest in a presidential battleground state embodies the current right-left divide in the US. 

- Republican Brian Kemp, the 55-year-old Georgia secretary of state, is narrowly ahead of his long-term rival with a 1.1-point lead according to the latest RealClearPolitics average.

- Democrat Stacey Abrams, a 44-year-old lawyer, would be the first black female governor in the history of the United States if she were to win in Georgia.  

- 2016: Trump 50.5 percent, Clinton 45.4 percent

Why it matters:

The Kemp-Abrams showdown is one of the most eagerly watched governor races. It has been the source of rampant controversy, not least because Republican Kemp is running for governor while controlling the election system in his current role as secretary of state. He denies accusations that he has attempted to suppress votes to sway the election, but in the wake of the 2013 Supreme Court decision to invalidate parts of the Voting Rights Act, this is one of the major issues in US politics. 

- Republican Mike DeWine, the 71-year-old Ohio attorney-general, trails by 4.7 points in the latest polling average. 

- Democrat Richard Cordray sat neck-and-neck with his opponent for several weeks, but the 59-year-old former head of the Consumer Financial Protection Bureau has stretched ahead in the final stages of campaigning. 

- 2016: Trump 51.3 percent, Clinton 43.2 percent

Why it matters:

The winner of the Ohio governor race will replace John Kasich, the 2016 Republican presidential candidate who is expected to challenge Trump in 2020. The president won the traditional bellwether by over eight points in 2016, but Democrat Cordray has a small polling lead going into election day. DeWine has faced a campaigning dilemma – stand with Trump and alienate moderates or with Kasich and put off the president's backers. In true political style, he's tried to do both. The matchup with Cordray is a rerun of the 2010 race to be state attorney general, a vote DeWine won by just one percentage point. 

- Republican Adam Laxalt holds a marginal polling lead going into election day, but the 40-year-old state attorney-general has failed to convince his own family -- 12 relatives co-wrote an opinion column declaring him the wrong choice for Nevada.  

- Democrat Steve Sisolak is behind in the polling average but ahead in several recent individual polls and is backed by former senator Harry Reid's campaign machine.

- 2016: Trump 45.5 percent, Clinton 47.9 percent

Why it matters:

Nevada hasn't had a Democratic governor in two decades, so it's no surprise the nail-biting contest has brought out high-profile surrogates from Trump to Obama. One person who has stayed out of the race is outgoing Republican governor Brian Sandoval, who refused to endorse Laxalt, part of a Nevada political dynasty, after he vowed to undo a commerce tax he put in place. A win in Nevada would be big for the Democrats, whose leadership have described the campaign run in the state as "the model."