LONDON:Democratic candidate Joe Biden was back as favourite to win the U.S. presidential election in online betting markets, a reversal of fortune for President Donald Trump who was favourite overnight, according to data from three aggregators.

The shift came after Biden overtook Trump in the battleground state of Wisconsin with an estimated 89% of the vote tallied so far. Trump has 49% and Biden has 49.3% of vote, according to Edison Research.

British-based Smarkets exchange is giving Biden a 58% chance, while New Zealand-based predictions market PredictIt had Biden at 63%. Trump's chances on Smarkets were sitting at 41% - a massive drop from 80% overnight.

Odds for a Biden win at one point had fallen to less than a third overnight on Tuesday, data from aggregators showed.

The flip in betting markets overnight was mainly "driven by Trump seemingly holding the key swing state of Florida as a result of a very strong showing for him in the Miami-Dade county with a large Cuban population," said Patrick Flynn, political analyst at Smarkets.

Trump earlier falsely claimed victory over Biden with millions of votes still uncounted in a White House race that will not be decided until a handful of states complete vote-counting over the next hours or days.

Bettors on British betting exchange Betfair meanwhile were also giving Biden about 60% chance to win, denting the prospect of a second term for Trump in the White House.

The 2020 election is shaping up to be the biggest betting event of all time, betting companies say, with one player on Monday placing a record-breaking one million-pound bet on a victory for Democratic challenger Joe Biden.