US president Bill Clinton arrived in Rhinebeck on the eve of daughter Chelsea Clinton's wedding, casually dressed and looking fit.

The former president pulled into upstate Rhinebeck in a black Suburban SUV around lunchtime, dressed casually.

"Today is the most beautiful day ever," Clinton declared after sharing a pasta lunch with brother Roger, another relative and a friend in the small upstate town.

The crowd let out a huge roar when Clinton - in a black polo shirt and jeans - exited GiGi Trattoria. His party of four took a back table at the local Italian restaurant.

"He looked trim. He lost the weight Chelsea asked him to lose," the New York Daily News quoted Julie Davis, an Albany actress, who ran into Clinton inside the eatery, as saying.

"I had just sat down for lunch and was ordering iced tea when I heard someone screaming, 'It's him, it's him!"

"I said, 'Gee, this is a pleasant surprise and congratulations.' He said, 'Thank you," Davis added.

"Thank you, thank you," Clinton told the crowd before leaving about an hour and 45 minutes after his arrival.

Clinton was flanked by the Secret Service when he arrived around the corner from the Beekman Arms Hotel, instantly drawing a huge crowd. (ANI)