Japan on Sunday hailed Naomi Osaka's stunning upset against the legendary Serena Williams to win the US Open, giving the nation some rare good news after a summer of deadly natural disasters.

Prime Minister Shinzo Abe led the praise, taking to Twitter to congratulate Osaka after her 6-2, 6-4 win in New York.

"Congratulations on your victory at the US Open. The first Japanese player to win a Grand Slam title. Thank you for giving energy and inspiration to the whole of Japan," the premier tweeted.

Abe was on his way to the northern island of Hokkaido where a massive earthquake last week sparked landslides that buried houses in a rural town, killing at least 35 people and injuring hundreds of others.

Osaka's grandfather Tetsuo Osaka, 73, lives in Hokkaido and said he wept watching his granddaughter on television.

"It still hasn't sunk in for me yet. The moment she won, my wife and I rejoiced together. I was so happy, I cried," he told public broadcaster NHK.

"I hope she stays healthy and continues her good work. I also hope she wins at the Tokyo Olympics (in 2020)," he said.

Fellow tennis star Kei Nishikori flooded Twitter with emojis of trophies, thumbs up and Japanese flags, followed by a simple tweet of "proud" alongside a Japanese flag.

And Tsuyoshi Fukui, a former top Japanese player and now senior official at the Japanese Tennis Association, said Osaka's performance would help to cheer the country up after typhoons, floods and earthquakes dominated the headlines this summer.

Osaka's "tenacious and patient performance ... must have been a great show of encouragement to those Japanese people who saw damage from such things as typhoons and earthquakes," Fukui told Japanese media.

Meanwhile, NHK took a break from its round-the-clock coverage of the disaster to turn to happier news.

"Osaka wins women's US Open, becomes first Japanese to win Grand Slam," blared the broadcaster's top headline.

Sports Nippon newspaper said Osaka had achieved a "complete victory" against an "irritated Serena who broke her racket".

The Asahi Shimbun daily said on Twitter it would be printing an extra edition and distributing it in Tokyo.

Pride of Japan

The final will probably be remembered for a meltdown from Williams who called the chair umpire a "thief" as much as for the 20-year-old's historic win.

Williams's tantrum overshadowed an outstanding performance from Osaka, who made her second career title a Grand Slam after winning her first at Indian Wells in March.

Osaka has dual Japanese-American citizenship and often replies to questions from Japan's media in English, apologising for not knowing the appropriate word when she speaks Japanese.

After earning $3.8 million (3.29 million Euros) for the victory, Osaka said her next goal was a simple one: to win her next tournament in Tokyo.

Asked if she was prepared for the reception she'll receive as the country's first Grand Slam winner, Osaka said: "Apparently not, because people keep asking me that."

Japan remains a fairly homogenous country and mixed race children -- especially those with black heritage -- can often face prejudice, although attitudes among younger generations are changing.

And Japanese fans on social media were happy to claim her as one of their own on the day of her greatest triumph.

"Her interview showed that she is clearly Japanese -- regardless of where she was born, where she grew up, the colour of her skin and the language that she speaks," said one fan on Twitter.

"You are the pride of Japan."