Amazon.com has increased its average starting wage in the US to $18 per hour and said it plans to hire more than 125,000 warehouse and transportation workers there.

The world's largest online retailer also said it would pay a sign-on bonus of $3,000 in some locations and the hourly wage could go up to $22.50.

Amazon was among the first few retailers to set a $15 an hour minimum wage in 2018 in the US.

Amazon had said in May it would pay around $17 in average wages.

The company is hiring to run the 100 logistics facilities it will launch this month in the US, on top of the more than 250 that opened earlier this year.

The additional staffing will also help roll out one-day delivery for Amazon's Prime loyalty club members.

Retailers are scrambling to hire hourly workers in a tight-labour market and have been offering benefits and sign-on bonuses to entice them.

Walmart said earlier this month said it planned to hire 20,000 workers at its supply chain division ahead of the busy Christmas season.