Fans of the Kansas City Chiefs and San Francisco 49ers were all smiles as they entered Allegiant Stadium for the Super Bowl, but admitted their good cheer came with a side of nerves.

Security was tight but fans arriving early for the NFL’s championship game said they had no issues getting into the $US1.9 billion stadium located just off the Las Vegas Strip.

“Everyone has been fantastic,” said Chiefs fan Kay Peca, who was attending her first Super Bowl as an early 70th birthday present.

“Fans of the other team have been great. We’ve had a couple little snarls, but for the most part we fist bump.”

Pop superstar Taylor Swift had arrived at the stadium to cheer on her boyfriend, Chiefs tight end Travis Kelce, adding another layer of excitement to the already highly anticipated match.

“When my students find out that I’m here and I’m in the same building as Taylor Swift, they’ll ask, ‘Did you get a picture? Did you give her a hug?’” said Todd Boden, an elementary school music teacher from Pennsylvania.

“No, we were in the same building and that’s as close as we’re going to get.”

Boden said fans of both teams were being “cordial”, but that it belied nerves on both sides.

With a win, the Chiefs would secure their second consecutive Super Bowl title and cement their status as the league’s latest dynasty.

A 49ers triumph would deliver a record-tying sixth Super Bowl title and first since 1995.