An Amazon employee sorts boxes before loading them onto trucks for shipping at Amazon.coms fulfillment Center in Fernley, Nevada.

Ken James | Bloomberg | Getty Images

Shares of Affirm on Monday closed up 46.67% after the buy now, pay later platform announced a partnership with Amazon.

The partnership, which was made available to some Amazon users Friday, will allow customers to break up purchases of $50 or more into smaller installments. It also marks Amazons first partnership with an installment player, though the company already offers installment options on some items.

The deal was announced Friday, sending Affirm shares up as much as 50% in after-hours trading. Analysts at Bank of America called the news an unambiguous positive, but said it highlights Affirms technological leadership and strong reputation in the BNPL market. The analysts also maintained a buy rating on Affirm.

Amazons entry into the buy now, pay later space comes as demand for the space continues to heat up, particularly among younger generations who are turning to BNPL platforms instead of traditional credit cards that often come with high-interest rates.

This month, Square announced it was entering the space through a $29 billion purchase of Afterpay. Bloomberg News previously reported Apple is also planning its own installment partnership with Goldman Sachs.

Some of the biggest companies in buy now, pay later space include Affirm, Afterpay and Klarna. Most of them do not charge interest.

Some Amazon customers will bear interest on purchases, CNBC previously reported. Affirms current partners include Walmart and Peloton.

Amazon shares closed up 2.15% on Monday.

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