Police have warned parents to be vigilant over reports that children are being contacted by strangers through a popular gaming app.

Children who play the Roblox app can be sent unsolicited e-mails through the its messaging feature, according to a Facebook post by Greater Manchester Police.

Their Facebook post read: "Notice to parents – if you have a child, there's a strong possibility you will have heard of the game Roblox. Please monitor your child's activity and check their inbox as there have been reports of strangers interacting with children."

Concerned parents have already shared the message 400 times in under two hours after it was published by police.

According to its website, the Roblox app does not have a minimum age limit but enforces strict privacy settings for children younger than 12.

In January, police said they were deeply concerned after they discovered half of children at a primary school in Kent used the app. Police also sent a letter to parents warning that users may receive 'inappropriate' messages and noted that they saw 'naked' characters in the game.

Roblox is a popular multiplayer 'sandbox' game which its creators describe as the "world's largest social platform for play" and is estimated to have at least 56 millions players monthly.

Although the game has been around in various forms since 2005 its popularity has exploded in recent years. The game, a portmanteau of the words robot and blocks, allows users to create in-game experiences using blocks, similar to Lego. Last year, it was estimated that it paid $30m to third-party game developers who had created games using its in-built engine.

The game is currently available on Xbox, iOS and other platforms, although its mobile gaming app has drawn the most concern.

Robox Corporation have not yet responded to IBTimes UK for comment, but previously stated that the company is "constantly assessing and improving trust and safety measures."