US President Donald Trump’s chances of re-election gained sharply overnight in online betting markets as Americans head to the polls on Tuesday, according to Betfair Exchange.

Trump’s odds of winning the election improved to 39 per cent from 35 per cent on the UK-based platform, while Democratic challenger Joe Biden saw his chances dip to 61 per cent from 65 per cent.

The election is on track to be by far the biggest betting event on record, with £300 million bet with the platform so far, Betfair said. It accepts bets right up until the result is announced and sees bets with it to hit the £400 million mark, double that of 2016.

Betters on British exchange Smarkets give Trump a 38 per cent winning chance.

Trump’s average odds on election day in 2016 sat at 5/1 (a 17 per cent chance) — 20 per cent lower than his odds now.

Biden has a substantial lead in national opinion polls, although the contest is slightly closer in battleground states likely to decide the race.

One person had placed a £1 million bet on Biden, Betfair said on Monday, the biggest political bet of all time. If Biden wins, the player would bag £1.54 million.

Moscow does not have inflated expectations for cooperation with the new US President, the RIA news agency said.