NEW YORK -- Amazon wants to make your impulse buys even more impulsive. The e-commerce powerhouse is offering free same-day delivery service in some cities to its Prime loyalty club members.

Amazon says starting Thursday more than 1 million items including books, electronics and vacation gear will be eligible for same-day delivery in 14 metro areas including New York, Los Angeles, the San Francisco Bay Area, Philadelphia, Phoenix and Atlanta. Orders over $35 are eligible for the service. They need to be placed by noon and will be delivered by 9 p.m.

Orders under $35 can still have one day delivery, it just costs $5.99.

Previously the service cost $5.99 for Prime members and $9.98 for non-Prime members for the first item, plus 99 cents for each additional item.

About 20 million items on the site are eligible for free two-day delivery for Prime members. Prime loyalty club membership costs $99 a year.

"We'll continue to make it faster and continue to look at different alternatives to give customers maximum flexibility," said Greg Greeley, vice-president of Amazon Prime.

Amazon in general has been expanding its Prime program's offerings in an effort to grow its membership with services such as grocery delivery, one-hour delivery in some cities, beefed up video streaming and the creation of a Bluetooth speaker called the Echo that syncs with Prime music.

On Tuesday, it announced it was hiring 6,000 full-time workers for its more than 50 distribution centres across the country.

The delivery sector is heating up with new startups challenging traditional delivery methods. Ride-hailing service Uber is testing local delivery service, and delivery service Postmates has begun working with restaurants like McDonald's and Starbucks, in addition to offering one-hour delivery services for most restaurants and stores in major metro areas.

Not to be outdone, last week Seattle-based Amazon said it would begin offering one-hour delivery from local stores in New York City's Manhattan borough.