Book shops across Sussex are bracing themselves for the launch of what seems certain to be the most successful Harry Potter adventure yet.

The Half-Blood Prince is the sixth in a series which has sold more than 200 million copies worldwide since 1997 and demand for the new volume is intense.

Retailers are allowed to begin selling the book at 12.01am on Saturday and many will be staying open throughout the night.

Lynn Ramzi, events co-ordinator of Asda in Hollingbury, Brighton, said, "Being a 24-hour store we will be open all night. It is going to be a massive event with long queues so we have organised plenty of entertainment to keep customers happy, including Harry Potter readings and fancy dress competitions."

The bookshop chain Waterstone's said yesterday that if its own advance orders were typical, 250,000 people would buy the adult edition of the book as soon as it was published.

This pattern was confirmed in online orders to the bookseller Amazon, which has already logged 1.4 million orders.

Waterstone's predicted the adult edition, sold at the same price as the children's, could account for as much as 30 per cent of total sales.

Callum McIntyre, 14, from the Dorothy Stringer School in Brighton said, "I am a massive Harry Potter fan and I can't wait for the Half-Blood Prince to come out, it will be great."

All retailers worldwide had to sign an embargo agreeing not to sell copies of the book before Saturday and its release has sparked a price war.

Asda will sell the book at £8.96, 47 per cent less than the recommended retail price of £16.99.

Meanwhile, the Kwik Save chain defended a price-cutting campaign on the book by announcing that, to ensure children could get copies, it would ban adult purchasers until 10am on Saturday unless they were accompanied by "genuine pint-sized Potter fans". It is selling copies at £4.99.

Ottakars in Horsham, which has set a price of £10.99 will be open from midnight on Friday and entertain customers and feed them "wizard cakes".

Laura James, sales manager of Borders, in Churchill Square shopping centre, Western Road, Brighton, said: "As yet our price for the latest Harry Potter book is unconfirmed."

Borders will stay open until 3am on Saturday, offering entertainment.

Libraries in Chichester and Crawley will stock the book from Saturday, staggering readings at Crawley library in Northgate Avenue, Crawley, at 10am and Chichester library in Tower Street, Chichester, at 11am.

Children are invited to dress up as their favourite characters.