The outcry over errant retailers at Sim Lim Square has been brewing for years.

But the furore hit a crescendo this week, after Vietnamese tourist Pham Van Thoai was seen crying while kneeling at mobile phone shop Mobile Air, begging for a refund.

He had been told to pay $1,500 for the warranty of a $950 iPhone 6 that he had paid for.

The incident came a week after the same shop refunded a Chinese student $1,010 in coins.

She had earlier been asked to pay $1,400 on top of the $1,600 that she had paid for an iPhone 6 Plus.

She took her case to the Small Claims Tribunal, which ordered the shop to refund her $1,010.

Following news reports on the incident, China's Ministry of Foreign Affairs posted a notice on its website on Wednesday, warning Chinese tourists about shopping for mobile phones in Singapore.

The notice said there had been many cases of fraud when Chinese tourists purchased electronic goods like mobile phones. It reminded tourists to look out for notices of errant retailers put up in the malls.

Sim Lim Square's notoriety worsened after Vietnamese media picked up on the plight of Mr Pham.

International news agencies such as Agence France-Presse and the BBC also reported on the incident and the story was picked up by major news websites in Britain and Australia.