Thousands of Cambodians have joined a procession to return what they believe are Buddha's relics to the mountaintop shrine from where they were stolen three years ago.

The golden urn containing the relics was placed in a decorated car and driven some 40 kilometers (25 miles) from the Royal Palace in Phnom Penh to the Oudong mountain shrine on Friday.

The reinstallation took place on a national holiday to celebrate Buddhism's holiest day marking the birth, enlightenment and death of Buddha.

Monks, government officials, students and laypeople joined the procession.

The urn was stolen from the shrine in 2013 and recovered a year later but was temporarily placed at the Royal Palace. Four guards at the shrine and one more person were arrested.