Gabby Douglas and Simone Biles are reigning Olympic and world champions in gymnastics, but meeting Jamaican sprint star Usain Bolt in Rio proved an overwhelming experience for the US teammates on Wednesday.

"He was very cool walking into the cafeteria, and Aly (Raisman) and Gabby (Douglas) just about flipped the dinner table and screamed 'It's Usain!' like little girls," said 19-year-old Biles, a record 10-time world champion tipped to be one of the stars of the Rio Games.

"I was like, 'You guys, you have to calm down; do you know what it's like to be in that position?' But it was very cool," said Biles, who is competing in her first Olympics.