Democratic Sen. Bill Nelson beat off a challenge by Rep. Connie Mack IV, a member of Florida's best-known political dynasty. Rep. Allen West, a conservative black Republican and Tea Party hero, was locked in a tight race.
Obama had 50 percent to 49 percent for his Republican challenger, The Miami Herald reported. The result mirrored the findings of an exit poll conducted for the newspaper by Edison Research.
State election officials reported Obama was leading by 53,000 votes. He had 49.9 percent of the vote to 49.24 percent for Romney.
Florida with 29 electoral votes is the nation's largest swing state. Obama carried it four years ago, and President George W. Bush did so controversially in 2000 and then again in 2004.
The final results were unlikely to be available until later Wednesday because tallying was suspended for the night in Miami-Dade County. But Obama did not need Florida to win the election.
The exit poll shows Obama won 60 percent of the Hispanic vote to 39 percent for Romney, the Herald said. He did slightly better than Romney among independents.
Democratic U.S. Sen. Bill Nelson defeated his Republican challenger, U.S. Rep. Connie Mack IV. Nelson had 55.2 percent of the vote to 42.3 percent for Mack.
Mack's campaign and outside groups spent $22 million trying to elect him to the seat once held by his father, The Miami Herald reported. Nelson, seeking a third term, spent about $5 million less.
Long lines and confusion were reported in South Florida, the Herald said. State election officials said everyone in line when polls closed at 7 p.m. EST or an hour later in the western panhandle would be able to vote.
Nelson is the only Democrat currently holding statewide office in Florida. The state went for Obama in the 2008 presidential election but appeared in late polls to be a tossup or leaning to Romney.
West held a slim lead over challenger Patrick Murphy, The Palm Beach Post reported. He was running in the 18th district on the east coast, which spans Palm Beach, St. Lucie and Martin counties.
West moved districts because his current one became majority-Democrat after the 2010 Census. The race was one of the most expensive for Congress this year with spending of about $23 million.
The congressman told supporters in Palm Beach Gardens late Tuesday he expected to win. Final results were not expected to be available until Wednesday at the earliest.
"We were outspent 4 to 1 or 5 to 1 but 50-50 right now," he said. "We're about to win this race."