Stars of High School Musical 2 have attended the European Premiere of the film at London's O2 Arena.
Fans chanted Zac's name for an hour before he appeared
Many fans gathered wearing cheerleader costumes and waving red pom-poms while some chanted Zac Efron's name for an hour before he arrived.
Speaking about his new-found fame, Lucas Grabeel - who plays Ryan in the movie - said: "It's really crazy and slightly unnerving, to be honest."
UK viewers can see the film on Disney on 21 September.
Around 17.2 million people watched it when it was broadcast in the US on 17 August.
Speaking outside the arena in Greenwich, Grabeel revealed he had recently watched Prince perform there.
"I was there as a fan and I felt what all these people feel being here now, it's fantastic and so great to be part of it," he said.
Vanessa Hudgens, who plays Gabriella, said she had found fame "kind of crazy".
Vanessa Hudgens said she had found fame "crazy"
The 18-year-old added: "It's overwhelming sometimes but it's great to be here. I'd like to say to my fans that they should never give up on their dreams."
Monique Coleman, 26, who plays Taylor, insists she is still a "regular girl, despite being a well-known actress now.
"I'm just me, I wake up every day and brush my teeth, for me it's really about the fans and this moment which changes their lives," she said.
The original film began life as a low-budget movie on the US Disney Channel, one of 10 such films the company produces every year.
The soundtrack became 2006's biggest-selling album in the US and led to a series of huge stage shows.