Amazon brought Prime to Southeast Asia a year ago when it kicked off its membership program in Singapore. Since then, its regional rivals have seen strong growth, and the American juggernaut has failed to take the lead, market observers told CNBC.

That doesn't necessarily mean Amazon is failing in what it set out to do. Rather, the development of Southeast Asian e-commerce is "still in early stages," according to Candice Ong, the chief commercial officer of e-commerce merchant Shopback.

When Amazon first launched in Singapore, Ong said, there was a lot of news and anticipation. “That is expected, given that they (are) a huge player,” said Ong, whose company has been an active participant in the growth of the region’s e-commerce sector by working with large companies such as Lazada and Foodpanda.

Amazon declined to comment for this story.

According to Ong, however, Amazon remains only one of several competitors vying for pole position in the region, with Chinese heavyweights such as Tencent and Alibaba investing in companies such as Sea Group’s Shopee and Lazada, respectively.