The 28-year-old Canadian actor-writer told The New Paper: "Though we've heard of Jay's massive popularity among the Chinese community, we didn't know how big he really was...(until we) witnessed it for ourselves."
"There was a huge crowd forming outside, including a bunch of Asian girls who were freaking out like they had just seen the Beatles.
Chou makes his Hollywood debut as Kato, the Green Hornet's agile sidekick.
The action comedy - which opens here on Thursday - also stars Cameron Diaz and Christoph Waltz.
During roundtable interviews with the media at St Regis Hotel, Rogen continued with a loud guffaw: "I have met a lot of famous people in my life, but I've never seen anything like that before (referring to the Chinatown incident)...It was pretty amazing."
The megawatt stardom of 32-year-old Chou was affirmed by Gondry, who gamely revealed that throughout the Asian promotional tour of The Green Hornet, Chou never failed to become "the main attraction".
"When we were in Japan and Beijing, no one showed interest in talking to me or Seth," said the 47-year-old Frenchman best known for the critically acclaimed Eternal Sunshine Of The Spotless Mind (2004).
"Even if they did, it was just to find out what it was like working with Jay." With a smile, Gondry added that among Rogen, Chou and himself, Chou "also gets the most number of female fans".
"It's kind of like The Rolling Stones," he deadpanned, making a reference to the legendary English rock band.
"All the girls love (frontman vocalist) Mick Jagger and (guitarist) Keith Richards and I am bassist BillWyman."
Rogen doesn't seem to mind the fact that Chou constantly overshadows him.
"Well, turns out he wasn't lying at all back in America," quipped the star of Hollywood comedies like Knocked Up, Pineapple Express and Funny People.
"He is indeed extremely famous!"
Chou landed the part of Kato after plans to get Hong Kong veteran actor Stephen Chow (who was slated to play Kato and take on directing duties) on board fellthrough.
According to Rogen, the first reading with Chou was done over Skype, and the film-makers instantly found him "very cool".
Despite Chou's popularity in the Asian leg of the film's promotional tour, there was nary a trace of rivalry between the pair.
Chou told TNP in Mandarin: "On this trip to Asia, I've been teaching Seth some basic Mandarin."
"Just the other day, I taught him 'chao diao', a colloquial term used in Taiwan that means awesome," said the Mandopop superstar, whose much-loved rap hit Nunchuks was made The Green Hornet's official end credits theme.
In return, Rogen taught him English phrases - the kind Chou had better not show off in public.
"Yes, I'm a very bad influence. I taught him the swear words, the stuff you'd consider slightly dirty," confessed Rogen sheepishly.
The language barrier between Chou and his Hollywood counterparts has not stopped them from falling in love with his distinctive R&B musical style.
Chou held a concert at the Los Angeles Memorial Coliseum and Sports Arena last month, one that saw the attendance of Gondry, Rogen and Diaz.
"I passed them my CDs as well," he said.
Well-known in Taiwan for his deftness in performing magic tricks, Chou recalled how he found it "awkward" showing off his skills in front of Rogen or Gondry as "it's not a very guy thing".
He added: "With Cameron, it's okay, she knows plenty of tricks herself, so I did promise her I'll learn some new ones to show her next time."
In response to a journalist's question about his concerns over being stereotyped as an Asian actor in Hollywood, Chou laughed and said: "If you've caught the movie, you'd know it definitely doesn't put Asians in a bad light.
"In fact, it shows Asians aren't to be bullied."
Chou's version of Kato, who was played by the late Bruce Lee on the small screen, isn't simply a sidekick of Rogen's Green Hornet, but a buddy and an equal.
"It's something we set out to achieve right from the beginning," said Rogen, who is also a co-writer for the film.
"To us, it's ridiculously insulting how Asians have always been relegated to the sidekick supporting role.
"If you look at the television series, you can't help but marvel how Bruce Lee was really iconic, yet subjugated as Kato."