When Channel NewsAsia tried to place an order at about 4.30pm on Thursday, a message featured prominently at the top of the landing page stated that delivery was currently unavailable.
In response to enquiries from Channel NewsAsia, an Amazon spokesperson said on Thursday: "We are thrilled to learn customers in Singapore love ultra-fast delivery as much as we do. Due to great customer response, delivery is currently unavailable. We encourage customers to check back soon."
The delivery service was down all night, and was still unavailable when Channel NewsAsia checked on Friday morning.
Amazon said on Friday that it was fulfilling "many thousands of orders" each day, and is working on opening up new delivery windows for customers.
The e-commerce giant's promise of free two-hour delivery with a minimum purchase of S$40 was expected to shake up the local online retail scene, taking on local delivery services by the likes of FairPrice Online and RedMart.
It also touted an offering of "tens of thousands" of products, comprising popular brands in Singapore, such as Milo, Tiger Balm, MamyPoko and Pampers - all housed in its 100,000-sq-ft urban fulfilment centre, reportedly the largest such facility in the tech company's stable.