Amazon has launched same-day delivery to Prime members across 1 million items in London and parts of Hertfordshire and Berkshire.

Unlimited same-day deliveries are free to those who pay the £79-a-year Amazon Prime subscription. The etailer added it is planning to expand the service into other areas of the UK “in the coming months”.

Prime members who place an order for same-day delivery by noon will receive their delivery between 6pm and 10pm the same evening.

There is no minimum order value to qualify for the service.

Amazon managing director Christopher North said: “We know how important speed of delivery is to our Prime customers and we’ve been continuing to invest in our delivery network to offer even more fast delivery options.

“We are excited to launch our newest benefit for Prime members – free same-day delivery on 1 million items. This is on top of all the other Prime benefits, like unlimited streaming of movies and music, unlimited photo storage and more.”

It represents the latest salvo in the growing war over fulfilment. In response, Argos has rushed out an announcement about offering same-day delivery for free.

The Argos initiative is part of a two-week promotion designed to encourage customers to carry out their Christmas shopping before Black Friday, the shopping bonanza that has been criticised for hitting retailers’ margins.

John Walden, boss of Argos owner Home Retail, last month already expressed concerns over the impact Black Friday will have on Christmas trading.

Argos will offer free same-day deliveries between tomorrow and November 24, but shoppers will only qualify for free delivery if they spend over £50.

The retailer is also attempting to drive take-up for its Fast Track in-store collection service by giving customers £1 back off orders over £25.

Argos marketing director Stephen Vowles said: “We are really hoping many customers may want to get the shopping in now before Black Friday and avoid those crowds.

“We are keen to generate a trial of Fast Track collection, so we thought the £1 off was a good nudge factor. That is quite innovative and new, and is not the direction of travel of our competitors, who are starting to charge for click-and-collect.”