Chinese online retail giants Shein and Temu have warned US customers that goods will get pricier from next week, after President Donald Trump imposed hefty tariffs on goods from China.

In almost identical statements, the rival companies said they have seen operating expenses rise "due to recent changes in global trade rules and tariffs", adding they will make "price adjustments" from 25 April.

The shopping sites have gained tens of millions of customers in the US, attracted by their ultra-low prices.

Their popularity has put pressure on Amazon, prompting it to launch a new platform called Haul last November, featuring items for under $20 (£15.10).

Since returning to the White House in January, Trump has imposed taxes of up to 145% on imports from China. His administration said this week that when the new tariffs are added on to existing ones the levies on some Chinese goods could reach 245%.

Trump has also ended a duty-free exemption for goods worth less than $800, which helped Shein and Temu make rapid inroads to the US market.

US lawmakers on both sides had raised concerns about how these companies had "exploited" the provision.

An estimated 1.4 billion packages entered the US under this arrangement last year, up from 140 million in 2013, according to US customs authorities.

Since Trump started imposing the tariffs, Shein and Temu have seen the ranking of their apps fall sharply.

Temu is now the 75th most downloaded free app on the US Apple Store, after having consistently taken one of the top five spots in the last two years. Shein is in 58th place, down from number 15 last month.

But other Chinese retail apps continue to be ranked highly in the US, including DHgate in second place and Alibaba's Taobao at number seven.

Shein and Temu have also slashed their advertising spending in the US.

Temu has "turned off all their Google Shopping ads in the US" as of 9 April, Mike Ryan, head of e-commerce insights at online advertising agency Smarter Ecommerce, said on LinkedIn.

Temu's average daily US advertising spend on social media platforms include Facebook, Instagram and YouTube fell by 31% in the two weeks leading to 13 April, compared with the past month.

Shein's average daily US ad spend fell by 19% over the same period, according to data from market intelligence firm Sensor Tower.

In their statements, Temu and Shein encouraged customers to shop before higher prices kick in.

"We stand ready to make sure your orders arrive smoothly during this time.

"We're doing everything we can to keep prices low and minimize the impact on you. Our team is working hard to improve your shopping experience," the statements said.

Temu and Shein did not immediately respond to requests from the BBC for further comment.