SINGAPORE - U.S. Treasuries tanked in volatile trade on Wednesday as investors worried that a possible Republican sweep of Congress and the White House could weaken the U.S. balance sheet.

The benchmark 10-year Treasury yield rose as much as 18 basis points to 4.471%, its highest since July, as results showed Donald Trump improving on his 2020 performance and Republicans winning control of the Senate.

Yields rise when bond prices fall, and Trump's plans for restricted immigration, tax cuts and tariffs are seen as negative for bonds on multiple fronts.

Tariffs are expected to stoke inflation and reduce the chance of rate cuts, while tax cuts would impact government revenues.

"I start to worry when yields cross the 4.50% mark," said Matt Orton, chief market strategist at Raymond James Investment Management.

"If we don't reverse that upward trend, I would be more reticent to add too much more risk until we hear from the Fed or get a little bit more guidance with respect to where terminal rates might lie."

In early results of a tightly contested U.S. presidential race, Trump defeated Democrat Kamala Harris in the battleground states of North Carolina and Georgia, Edison Research projected, and showed strength across broad swaths of the country.

The outcome remained uncertain in five other states expected to determine the winner.

Treasury yields had already got off to an early surge after online prediction markets favoured Trump over Harris for the nation's top job.

The two-year yield peaked at 4.309%, its highest since August, and last traded roughly 5 bps higher at 4.2596%.

Yet, while markets seem to be front-running the possibility of a Republican sweep, such an outcome is far from certain and raises doubts about how much of Trump's tax cut plan will make it through Congress.

U.S. budget deficits and government debt levels were largely projected to surge under either candidate in the election, according to several estimates, although Harris was expected to add less debt than Trump.

The Committee for a Responsible Federal Budget, which advocates reducing federal deficits, estimates Trump's spending plans would add $7.5 trillion to deficits over 10 years.

Ten-year yields rose almost 50 basis points in October, when markets were pricing in a higher likelihood of a Trump win.

"The biggest issue is if Trump or Harris are going to get full mandates," said Arnim Holzer, global macro strategist at Easterly EAB Risk Solutions in Pennsylvania. "If they don't get blue or red sweeps, it limits the fiscal damage, and that's the best outcome for bondholders."

Trump's proposals would also tend to push up the dollar and potentially limit how far U.S. interest rates might ultimately be lowered.

The Federal Reserve kicks off its two-day monetary policy meeting on Wednesday and is expected to deliver another 25-basis-point rate cut, though a potential Trump victory could complicate the U.S. rate outlook.

Traders have since reacted to the election results by trimming bets on Fed cuts next year, with rates seen staying above 4% until May 2025.

In other maturities, the yield on the 30-year Treasury note last traded 10.8 bps up at 4.5582%, after having hit its highest level since July earlier in the session.

Its five-year counterpart similarly peaked at a four-month high of 4.3290%.

(Reporting by Rae Wee in Singapore; Editing by Christopher Cushing and Shri Navaratnam)