Fencing gold medallist Edgar Cheung Ka-long said Hong Kong had gone "insane" after he won the Chinese territory's first Olympic gold in 25 years and only its second ever.

The 24-year-old stunned Italy's reigning Olympic champion Daniele Garozzo 15-11 in the final of the men's foil at the pandemic-delayed Tokyo Games.

Hong Kong's only previous Olympic gold came at the 1996 Atlanta Olympics, when Lee Lai-shan won a gold medal in windsurfing.

Cheung might have appeared calm in victory but he said he was anything but.

"To be honest, I'm not that calm, I don't know what I can do," he said after claiming gold on Monday.

"It's like a dream -- that's why everyone thinks I'm calm, but I didn't know what happened."

Aside from the two gold medals, Hong Kong's only other previous Olympic medals were silver in 2004 at Athens in table tennis and a bronze in cycling at London 2012.

"The reaction in Hong Kong has been insane," said Cheung, who is in line to pocket five million Hong Kong dollars ($600,000) from the city's government as a reward.

"Because in total medals in Hong Kong, we only have three. Now we have four because we haven’t had a gold medal since 1996 so it means a lot to show to the world we can do it," Cheung added.

"We are not only a city. We can fight for victory."

Good news for troubled city

The last time Hong Kong won gold at the Olympics it was still a British colony and the anthem played for windsurfer Lee was "God Save the Queen".

Hong Kong was handed back to China a year later -- the same year Cheung was born. And when Cheung stood on the podium on Monday night it was China's "March of the Volunteers" anthem that played.

Cheung's victory is a much needed dose of good news for his troubled hometown.

Huge and often violent democracy protests convulsed the city two years ago. China has responded with a crackdown on dissent and an official campaign to root out anyone deemed unpatriotic.

Hundreds of fans crowded into a mall on Sunday night to watch Cheung's final bout on a large screen, bursting into cheers after he won, some popping champagne corks.

When China's national anthem played at the medal ceremony it was drowned out with rhythmic chants of "We are Hong Kong" from the mall crowd.

Hong Kong's pro-Beijing leaders seized on the victory with a flurry of congratulatory statements, including from chief executive Carrie Lam who video called Cheung.

"We are thrilled that with his outstanding skills and calmness as well as perseverance in adversity during the competition, he has succeeded in making history for Hong Kong," she said later.

Pro-democracy activists, many of whom have fled overseas during China's crackdown, also jumped on Cheung's win.

Activist Frances Hui posted a video of Cheung's medal ceremony with China's anthem replaced by a popular pro-democracy protest song.

Nathan Law, a prominent democracy leader who fled to Britain last year, wrote: "Thank you Ka-long for telling Hong Kongers who are facing a low point that effort and persistence are definitely useful.