Colourful myths and legends will come alive on Nelson streets tonight when thousands of people turn out for the city's Masked Parade.

The 18th annual parade - a centrepiece of the Nelson Arts Festival - starts at 5.30pm from Montgomery Square.

The masked throngs will complete a central city loop before returning to the square.

A total of 4300 people have registered to walk in the parade, making it one of the biggest ever, said Arts Festival director Sophie Kelly.

She expected thousands of spectators would also line the route: "It's Nelson's biggest community celebration."

This year's Masked Parade theme is myths and legends.

While it was just a guideline, Ms Kelly said organisers were "encouraging people to see how far they can explore it".

The parade will be followed by the More FM Carnivale and Sonic Live Zone at the top of Trafalgar St, with the party scheduled to run until 11pm.

The Carnivale will feature performances from headline act Tahuna Breaks as well as from the 2012 Smokefree Rockquest winners, New Vinyl, and finalist, Oh Blok (formerly Speaking in Silence).

Ms Kelly said this year's layout would be slightly different from previous years, with the main stage being set up at the foot of the cathedral steps.

Another difference will be that the popular Ferris wheel will not be included as it is being used at an A&P show elsewhere.

However, there will be a number of food stalls, and other street entertainment such as climbing walls, a silent disco, the Amazing Travelling Photobooth, and a wacky hair and makeup stall.

Ms Kelly said festival organisers have been working with police and other agencies, such as St John, HYPE, and private security, to ensure tonight's event would be safe and enjoyable for everyone.

As part of this they will be enforcing a strict liquor ban.

"We've put that message out to ask people, especially young people, to respect that."

The weather is forecast to be fine but people might like to wrap up warm as the temperature was expected to get down to 4 degrees Celsius overnight.

Organisers will announce a cancellation or any updates on the festival website and Facebook page, should the weather turn nasty.

- © Fairfax NZ News