Tickets on sale on Friday: Harry Potter and the Cursed Child run extended to April 2017 as touted tickets go on sale for £3,000

Harry Potter and the Cursed Child will extend its run after 175,000 tickets were sold within eight hours on the first day of booking, despite many struggling with technical ticket-sale problems.

A representative for the play said that customers would be able to for three extra months' worth of tickets, until 30 April 2017, after priority customers – those who had pre-registered – were given access to the latter four months of the play's eight-month run yesterday. Originally, these later tickets were to be reserved for the public booking that opens on Friday.  

The producers called the sales "unprecedented for a theatre production." In 2014, 100,000 tickets sold for Benedict Cumberbatch's Hamlet within three hours, making it the fastest-selling in theatre history. 

Customers were left frustrated by glitches with the ticket-sales system, which led to people losing tickets they thought they had bought and also being overcharged.

It's likely that demand will be even higher on Friday, when the remaining tickets go on sale to the public.

The producers have said the additional "booking period", or extra dates, would "ensure customers are given the best possible chance to obtain tickets." Details of this are expected to be released on Thursday. 

Despite the producers' warning against re-selling tickets, many that were sold yesterday quickly appeared on the secondary market for prices up to £900.

By Thursday morning, the cheapest pair of tickets available on ticket resale website Viagogo was £3,100 – for the dress circle of the theatre, originally priced between £100 and £160.

On rival website Stubhub, tickets in the balcony, the cheapest part of the theatre, were selling for upwards of £1,275.

As Harry Potter and the Cursed Child consists of two parts, customers may have to buy two tickets each in some cases.

The producers state on the play's website: "We reserve the right to refuse admission to customers with tickets purchased on re-sale websites.

"Tickets purchased through either of our official ticketing platforms must not be sold or advertised for sale on the internet, in newspapers or elsewhere. Any ticket advertised for sale in this way will be automatically void.

"Please note, the credit and debit card that you used to purchase your ticket, or confirmation email will be required as proof of purchase when you get to the theatre."