BEIJING, Feb 29 (Reuters) - Major Chinese third-party retailers JD.com (9618.HK) TMall, and Pinduoduo (PDD.O) are battling for customers by offering more steep discounts on Apple's (AAPL.O) iPhone 15 just five months after launch, as the US tech company suffers slowing sales in China.

The latest round of discounting comes after online retailers in October offered similar substantial discounts. Third-party retailers are also offering discounts of as much as 10% on Apple's iPhone 14 Pro.

Apple occasionally allows partner vendors in China to offer discounts on its phones to spur demand. The iPhone 15 launch came at a time of slowing sales for Apple in China where it faces rising competitive pressure from domestic rivals like Huawei (HWT.UL) and Xiaomi (1810.HK).

Last month, Apple offered discounts on iPhones on its official sites by up to 500 yuan in an unusual move.

On Thursday, the third-party retailers were offering discounts on all four models of the iPhone 15 series, including the iPhone 15, iPhone 15 Plus, iPhone 15 Pro and iPhone 15 Pro Max, Reuters checks showed, with some models on sale at up to 1,300 yuan ($180.68) less than the usual price.

Local media reported the price cuts and the three online retailers have branded the discounts as part of the upcoming International Women's Day campaign which falls on March 8th, but have not said how long the promotions will last.

Apple, JD.com, Alibaba (9988.HK) which operates the Tmall platform, and PDD didn't immediately respond to a request for comment.

The retailers have been engaged in a "value for money" battle as consumers tighten their belts in a slowing economy, with discounting a focus during some of the major shopping holidays and events.

According to checks made by Reuters, Pinduoduo is offering the 128GB version of the iPhone 15 for 4,588 yuan on their website - 1,411 yuan less than Apple's retail price of 5,999 yuan.

The 256GB iPhone 15 Pro Max, which typically retails for 9,999 yuan in Apple's store, can be purchased for 8,899 yuan on JD.com's flagship e-commerce platform.