The largest gathering of Hindus outside India is due to take place with 75,000 people set to take part.
Celebrations marking the 5,000-year-old festival of Janmashtami are to take place at the Bhaktivedanta Manor Hare Krishna temple in Watford, Herts.
The festival marks the birth of Lord Krishna, the most highly venerated God in the Hindu pantheon.
Organisers have erected 20 marquees on 77 acres near the temple, where plays and dancing will be held.
Although the festival starts at midday, the crux of the celebrations will be at midnight, the official time of Lord Krishna's birth.
Until then, many Hindus will fast all day.
The free festival, which runs until Sunday, is being overseen by 800 organisers who have spent the last month preparing for the event.
Co-ordinator Ramesh Kallidai said: "It is an amazing festival full of colour and warmth."