George Santos adresses reporters
US Congressman George Santos speaks to reproters as he leaves Federal Court on May 10, 2023 in Central Islip, New York. Michael M. Santiago/GETTY IMAGES NORTH AMERICA via AFP

Voters in suburban New York picked a Democrat to replace expelled Republican congressman George Santos on Tuesday, US networks projected, after President Joe Biden's party poured cash into TV ads to flip the seat in an election year.

CNN and NBC News both called the race in favor of Tom Suozzi, forecasting that he had defeated Republican Mazi Pilip in the election, which was marked by a heavy snowstorm across the district.

Suozzi, a veteran politician who previously held the seat and quit to unsuccessfully run for New York state governor, will serve out the remaining 11 months of the scandal-plagued Santos' term in the House of Representatives.

The win chips away at the Republicans' narrow majority in the lower chamber of Congress.

"Thank God," Suozzi said in a victory speech in Woodbury after the race was called. A crowd of supporters began chanting his name as protesters holding Palestinian flags briefly stormed the stage, shouting "genocide."

"Despite all the lies... about Tom Suozzi being the godfather of the migrant crisis... despite the dirty tricks... we won."

New York City Mayor Eric Adams, a Democrat, said Suozzi's victory "was good news for New York."

"We are fighters, I called my opponent and congratulated him," Pilip said in her concession speech in East Meadow.

Pre-election polling had showed that the race was tight, with Democrats reportedly spending $14 million on advertising and the Republicans $8 million.

Aggressive attack ads were used by both sides, with Republicans seeking to paint Suozzi as soft on illegal immigration, while Democrats characterized Pilip as against abortion rights.

Migration and abortion are central political issues as the United States limbers up for November's presidential election set to pit Biden against Donald Trump in a re-run of the 2020 contest.

One attack ad showed archive footage of Suozzi apparently boasting that he fought to keep immigration enforcement officers out of Nassau County, where a large part of the congressional district is located, when he was the area's top elected official.

Anti-Pilip ads suggested she would seek a nationwide ban on abortions.

Deep snow in New York's third congressional district, which includes small parts of Queens and Long Island's wealthy North Shore in Nassau, threatened to deter voters as authorities warned against driving.

Both Suozzi and Pilip's campaigns responded by offering a dial-a-ride service for voters, while there were media reports that the Republicans paid for plows to clear roads in areas sympathetic to the party.

Santos became only the third person to be ejected as a US lawmaker since the Civil War, in a rebuke previously reserved for traitors and convicted criminals.

He had won a House seat in 2022, helping the Republicans secure a tiny majority, but it quickly emerged that his backstory was largely a fabrication.

Santos, who has denied criminal wrongdoing, allegedly used donor money for Botox treatments and the OnlyFans porn website, as well as luxury Italian goods and vacations, according to the committee that investigated his conduct.

While the constituency backed Biden in 2020, Republicans took several seats in the area in 2022 and have an effective local operation to get out the vote.