A record 123.4 million people tuned in for the Super Bowl which saw the Kansas City Chiefs beat the San Francisco 49ers 25-22 in an overtime nailbiter, the game's broadcaster has said.

"CBS Sports' coverage... delivered the most-watched telecast in history with a total audience delivery of 123.4 million average viewers across all platforms," the network's parent company Paramount said in a statement late on Monday.

Viewership was "up 7 percent vs. last year's Super Bowl which was the previous record (115.1 million)... 202.4 million watched all or part of Super Bowl LVIII across networks."

Paramount said 120 million people watched the NFL championship game on CBS alone, a record for a single US network.

Chiefs quarterback Patrick Mahomes found Mecole Hardman in the end zone deep into overtime to seal a dramatic win in what was the longest Super Bowl in history.

The victory makes Kansas City the first team to win back-to-back Lombardi Trophies since the New England Patriots in 2003-2004, cementing the franchise's right to be regarded as the NFL's newest dynasty.

Usher led an all-star cast that included Ludacris, Alicia Keys and Jermaine Dupri for the half-time show.

Taylor Swift was the night's most-watched fan as she cheered on her boyfriend, Chiefs tight end Travis Kelce, from a luxury box with a coterie of famous friends including the rapper Ice Spice.

Swift's relationship with charismatic star Kelce has been a boon to television ratings, her every move offering headline fodder. (AFP)