The protesters said they decided to take action because the government refused to crack down hard enough. "Mainlanders are taking Hong Kong's resources to a frightening extent but the government has not been protecting our rights," spokesman Vincent Lau said.

"If the government solved the problem we wouldn't hate mainlanders so much."

They called for limitations on mainlanders travelling to Hong Kong under the individual-visitor scheme.

A mother from Kwun Tong who has been affected by the rush on baby formula signed a petition to support the group's campaign.

At the end of last year, shops in her neighbourhood were cleaned out of stock for two weeks and she almost ran out of milk to feed her 17-month-old son.

"I've seen people snapping up 40 cans at a time," said Chan Ching-yee. "I had to get my mother, brother and a neighbour help me scramble for it."

The protestors also went to a PrizeMart store in Mong Kok and shouted at shoppers who they suspected were mainlanders.

The shop is known to be popular with mainlanders stocking up on snacks and other goods.

In mid-September, hundreds of people protested at Sheung Shui MTR station, resulting in ugly scenes and scuffles with parallel traders.

Secretary for Food and Health Dr Ko Wing-man said yesterday the overall supply of baby formula in the city was enough for now but he would closely monitor the situation in the next few days. "We are concerned if mothers are having difficulty buying milk formula," he said.

"I won't rule out more severe measures, but that could bring its own negative results."