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Amazon Inc. (AMZN - Get Report) shares shed more than $40 billion in early trading Friday after the world's biggest online retailer posted record Christmas sales but forecast first quarter revenues that missed analysts' forecasts.

Amazon said earnings for the three months ending in December surged to $6.04 a share, well ahead of the consensus forecast of $5.68, as sales rose 20% to a record $72.4 billion. However, the group also guided for first quarter sales in the region of $56 billion to $60 billion, missing the Refiniitv estimate of $60.77 billion, citing regulatory uncertainty in India, a key growth market, raising questions over its uneven international strategy.

"There is much uncertainty as to what the impact of the government rule change is going to have on the e-commerce sector there," CFO Brian Olsavsky told investors on a conference call late Thursday, in reference to new rules that restrict foreign-owed companies from selling good through vendors in which they have an ownership stake. "We remain committed to complying with all laws and regulations, we will, but we're evaluating the situation."

"We feel very good about the long term prospects in India and doing a good job for both Indian customers and Indian sellers. The new regulations (must not have) unintended consequences," he added. "And again, I don't think it's necessarily consistent with better price, better selection and better convenience for the Indian customer."

Amazon shares were marked 4.27% lower at the start of trading Friday to change hands at $1,645.34 each, a move that trims the stock's three-month gain to around 2.8% and values the Seattle, Washington-based group at around $800 billion.

The international weakness overshadowed an otherwise bullish outlook from Amazon, which sees 2019 operating earnings in the range of $2.3 billion to $3.3 billion, some 73% higher at the top end when compared to last year's total.

Amazon is expected to ramp-up investment spending this year, however, owing to larger wage costs linked to its move to a $15 per hour minimum wage in the United States, its ambitions to challenge Netflix (NFLX - Get Report) and others in premium video content and increasing delivery costs tied to higher oil and gas prices.

Despite the concerns linked to Amazon's core retail business, the group's Amazon Web Services division continues to produce impressive results, with four quarter revenues rising 45% to $7.43 billion, taking the 2018 tally past $25 billion for the first time on record.

"n a lot of ways, 2018 was about banking the efficiencies of investments in people, warehouses, infrastructure that we had put in place in 2016 and '17. So while we'll continue to concurrently drive growth and customer offering and Prime benefits, we certainly do take costs seriously and we will continue to work on operational efficiencies," Olsavsky said. I would expect these investments to increase relative to 2018 and we've reflected what we see so far in Q1 in our guidance."