More than 12,500 people have petitioned US President Barack Obama to help Hong Kong avoid a baby formula shortage, saying infants in the city are facing malnutrition due to mainland Chinese "smugglers".

Formula is popular with mainlanders because of concerns about the safety of food processed in China following a series of scandals, notably in 2008 when six babies died from drinking milk tainted with the chemical melamine.

The appeal, labelled "Baby Hunger Outbreak in Hong Kong, International Aid Requested", was posted on Tuesday on the "We the People" section of the White House website, which does not require petitioners to be US citizens.

The number of signatures has to reach 100,000 by the end of the month in order to trigger a response from the Obama administration.

"Local parents in Hong Kong can hardly buy baby formula milk powder in drugstores and supermarkets, as smugglers from mainland China storm to this tiny city to buy milk powder and resell for huge profits in China," the appeal said.

"We request for international support and assistance as babies in Hong Kong will face malnutrition very soon," it added.

A city official said this week that Hong Kong was considering designating baby formula a "reserved commodity" to ensure sufficient supply.

It was not immediately clear what the anonymous author of the petition wanted Obama to do but Internet users in Hong Kong saw the appeal as an attempt to embarrass the government into action.

"The whole world will be laughing at Hong Kong for this," a mother on one popular baby forum said, the South China Morning Post reported.

Hundreds of mainlanders have been stuffing tins of baby milk powder into large bags and boxes near train stations at the border in recent days, ahead of the Lunar New Year holiday.

The majority of them are the so-called parallel traders who travel to Hong Kong by train and dodge import tariffs on their return.

Although the former British colony was returned to Chinese rule in 1997, it maintains a semi-autonomous status with its own laws and immigration controls.

Hong Kong is not the only place affected. Reports in Australia this month blamed Chinese customers for a shortage of formula in supermarkets and pharmacies, causing some outlets to ration sales.

Other recent petitions on the White House website to have grabbed the headlines include one requesting the government build a Star Wars-inspired "Death Star" by 2016 to "spur job creation" and strengthen national defence.

More than 34,000 people signed the appeal but the government rejected it last month with a tongue-in-cheek response saying "the administration does not support blowing up planets".

"Why would we spend countless taxpayer dollars on a Death Star with a fundamental flaw that can be exploited by a one-man starship?" it added.

Days later it quadrupled the number of signatures needed for an official response from 25,000 to 100,000, citing increasing online participation.

Other current petitions call for looser regulation of cigars, the legalisation of marijuana and the minting of a $1 trillion coin.