A new monument was unveiled in John Lennon's home town of Liverpool Saturday to mark what would have been the music legend's 70th birthday, aimed at promoting his vision of world peace.

The ceremony was attended by Lennon's son Julian and his first wife Cynthia in a park overlooking the River Mersey in this northwest English city, where the singer-songwriter and his fellow Beatles launched their careers.

It was one of a number of events planned worldwide to celebrate Lennon's legacy on his birthday, 30 years after he was shot dead outside his Manhattan apartment in December 1980.

"We come here with our hearts to honour Dad and to pray for peace and say 'thank you' to each and every one of you, and everybody involved in the celebrations today," said Julian Lennon, 47.

His 71-year-old mother Cynthia, who met Lennon at Liverpool Art College, added that people should not mourn him but should enjoy his life.

"Don't be morbid, enjoy the joy that he had and what we all have from his music," she told the crowd of dignitaries and fans from all over the world who gathered in the city's Chavasse Park for the unveiling ceremony.

The monument, designed by US artist Lauren Voiers and commissioned by a US arts organisation, the Global Peace Initiative, comprises a globe with multicoloured symbols of peace and musical references swirled above it.

There are two hands outstretched to the sky, doves of peace, a keyboard and a white feather, which Julian Lennon said was a symbol of his father's spirit.

"One of the things my father said to me was that should he pass away, if there was some way of letting me know he was going to be OK, it was by, in some shape or form, presenting me with a white feather," he said.

The unveiling of the monument kicks start two months of events in Liverpool aimed at celebrating Lennon's life, from the anniversary of his birthday to the anniversary of his death on December 8.