Amazon.com Inc.’s (AMZN) push into Southeast Asia is off to a rocky start after users couldn't access Prime Now, it’s same-day service.

The ecommerce giant entered the market for the first time on Thursday offering consumers in Singapore access to Prime Now and putting Alibaba Group (BABA), its Chinese rival, on notice. But a few hours after going live, consumers in Singapore were running into problems getting their purchases delivered. CNBC reported users couldn't select a window of time for their delivery, getting a message saying that deliveries for the remainder of the day and Friday were unavailable. The message more recently said “working hard to open up more capacity as soon as possible,” CNBC reported. What’s more, some of the items for sale were either sold out or out of stock. (See also: The Next Amazon-Alibaba Battle Will Be Fought in Southeast Asia.)

In a statement to CNBC, Amazon said the problems were a result of the retailer selling out of delivery availability. "Due to great customer response, delivery windows are currently sold out. We are rapidly opening up new windows to ensure we can continue delighting customers in Singapore," it said in the statement. Still, customers in the region didn't seem happy to accept that answer, at least on social media, where users were quick to express their frustration.

Foothold in Singapore

On Amazon’s Prime Now page on Facebook, several customers complained, with one Patricia Yeo putting it this way: “Are you kidding me? Is this really Amazon? Just launched and I couldn't even do a checkout since last night till now because you do not have any delivery windows??? I don't even need 2-hours and am not even buying grocery! It's fine even if it takes a day or 2 to deliver, but you advertised as 2-hour and we cannot even checkout since launch! Really leaves a bad taste…” Among the 37 comments left on the Facebook page most were unhappy with the outage.

In what is seen as a direct assault on Alibaba, the Seattle-based company said that Prime Now consumers in Singapore will get delivery on tens of thousands of items within two hours for free if customers spend 40 Singapore dollars (about USD$30) or more. For orders under that threshold, two-hour delivery is S5.99. Customers can also get their Prime Now order with one-hour delivery for S$9.99. The same-day delivery covers items such as milk, eggs, beer, fresh produce, toys and consumer electronics to name a few. The feature is part of its Prime membership that gives subscribers free shipping, among other perks. (See also: Lazada Teams Up With Uber, Netflix to Challenge Amazon in Asia.)

It’s no surprise the U.S. ecommerce giant would set it sights on Southeast Asia, which is expected to be the next area of growth for ecommerce. It has a growing number of internet users who are starting to embrace online shopping. A report from Google and Temasek Holdings, the Singaporean investment firm, forecasts the internet economy in Southeast Asia will increase to $200 billion by 2025, driven in a big part by ecommerce. While Amazon is blaming the early problems in Singapore on outsized demand, it’s not clear if this will hurt its reputation in the region, paving the way for rivals to capitalize.