Julia Balk spreads petals on the Imagine mosaic in Strawberry Fields in New York's Central Park on Saturday, which would have been John Lennon's 70th birthday. (Tina Fineberg/Associated Press)

Fans around the world marked what would have been the 70th birthday of John Lennon.

The ex-Beatle and peace activist was gunned down 30 years ago outside his apartment building near Central Park in New York City.

A large crowd gathered at Central Park's Strawberry Fields, where there is a memorial.

"His music speaks to people of any nation, any age, and that's why I think so many young people now who never would have known him still find him so appealing," said Karen Kriendler Nelson, 69, who lives nearby. She joined a group of fans who sang verses of Lennon's song Imagine.

'The values Lennon defended are still alive.'—Joan Acarin, Spanish tourist to New York

Tourists Joan and Jaia Acarin from Spain decided to visit the memorial during their trip.

"The values Lennon defended are still alive," said Joan, 41, from Barcelona. "It's the idea that we do not have to fight wars."

There's also a free screening in the park of LENNONYC, by Michael Epstein, with concert footage and home movies documenting Lennon's life in the city. The film is slated to air on PBS on Nov. 22.

Also on Saturday night, a charity concert to benefit Amnesty International at a music hall in Manhattan pays tribute to Lennon. Headlining the show are The Quarrymen, the founding members of Lennon's original band, who have reunited to play this special concert.

Celebrations began on Friday. The Rock and Roll Hall of Fame and Museum in Cleveland dedicated a time capsule in honour of Lennon containing several CDs, DVDs and books, and two notes written by his widow Yoko Ono.

The capsule will be opened in 2040, on the musician's 100th birthday.

A peace monument was also unveiled in Lennon's hometown of Liverpool on Friday, with his first wife, Cynthia, and son Julian on hand to mark the occasion. They also joined in the singing of Give Peace a Chance.

"I think the mourning is over for John. I think it's time to celebrate," said Cynthia, 71.

The towering steel sculpture featuring a globe with doves is inscribed with the statement: "Peace on Earth for the Conservation of Life. In Harmony of John Lennon 1940-1980."

Ono in Iceland

Ono — who has encouraged fans to post videos on YouTube in honour of her husband — is in Iceland, attending the annual lighting ceremony at the Imagine Peace Tower on the island of Vioey.

The artist, who is also performing with the Yoko Ono Plastic Ono Band in Reykjavik, posted a video message from Iceland on Saturday:

"[John] managed to turn his pain around to give the world many beautiful songs and important messages which changed our heads and the way of our lives," the 77-year-old widow said on the video.

"And I now see you are all celebrating his birthday today, to thank him for giving us so much in his short and intense life on this planet. I know John was not expecting so much love to still come from you. But he would have been very happy to know it. Thank you, thank you, thank you."

With files from The Associated Press