Amazon.com's lay-offs will increase to more than 18,000 roles as part of a workforce reduction it previously disclosed, chief executive Andy Jassy says.

The lay-off decisions, which Amazon will communicate starting January 18, will largely impact the company's e-commerce and human-resources organisations, Mr Jassy said in a public staff note on Wednesday.

The cuts amount to 6 per cent of Amazon's roughly 300,000-person corporate workforce and represent a swift about turn for a retailer that recently doubled its base pay ceiling to compete more aggressively for talent.

Amazon has more than 1.5 million workers including warehouse staff, making it America's second-largest private employer after Walmart.

Its stock rose 2 per cent in after-hours trade.

Mr Jassy said in the note that annual planning "has been more difficult given the uncertain economy and that we've hired rapidly over the last several years".

Amazon has braced for likely slower growth as soaring inflation encouraged businesses and consumers to cut back spending and its share price has halved in the past year.

The company began letting staff go in November from its devices division, with a source telling Reuters at the time it was targeting around 10,000 cuts.

The tech industry shed more than 150,000 workers in 2022, according to tracking site Layoffs.fyi, a number that's continuing to grow.

Salesforce said on Wednesday that it planned to eliminate about 10 per cent of staff, which numbered nearly 8,000 as of October 31.

The reversal of Amazon's fortunes has been stark.

It changed from a business deemed essential during the pandemic for delivering goods to locked-down homes, to a company that overbuilt for demand.