'Diablo Immortal' has been delayed suddenly in China.

Blizzard's free-to-play mobile and PC action role-playing game was due to launch on June 23 in the region, but just three days prior to the release date, a notice on China's 'Diablo' website explained that there are several reasons for the setback, including "a number of experience, network and performance optimisation" issues which need improving.

The statement read: “We are sorry to inform you that Diablo: Immortal’s scheduled launch on June 23rd will be delayed.

“The development team is working on a number of optimisations to the game – greater device support for a wider range of models, maximum graphics quality on more models, a number of experience, network and performance optimisations and more.

“We believe that the game experience will be smoother in the official launch version, bringing you better game content.”

A new release date is yet to be confirmed.

Meanwhile, Blizzard recently declared that the game achieved the "biggest launch in franchise history".

The MMO game was released on June 2 on iOS and Android, and had a whopping 10 million installs in just one week.

The official Diablo Twitter page tweeted: "Shoutout to the heroes of Sanctuary.

"In just one week, Diablo Immortal is the biggest launch in franchise history.

"Thanks for slaying with us."