Soaring demand from middle-class mainland parents hoping to pay less for imported infant formula is boosting cross-border milk-powder shipping from Hong Kong into the Pearl River Delta. At the same time, supermarkets are struggling to replace infant food made by blacklisted dairy firms. Couriers buying low-duty imported milk powder from Hong Kong and reselling it to affluent parents for a fee said yesterday that business had doubled or even tripled, and their supplies were about 15 per cent cheaper than those in mainland supermarkets. With more parents and transporters buying trusted foreign formula from Hong Kong, Shenzhen customs loosened its milk-powder quota for individual cross-border travellers to 24 tins this week. Fang Zhizhi, a Shenzhen courier ferrying imported milk powder for 10 yuan (HK$11.39) per tin, said orders from parents had doubled after major mainland dairies were blacklisted. 'Orders have jumped from a dozen to up to 50 tins a day and well beyond my capacity. I'll have to reject some of the orders.' Imported formula 'distributor' Wang Zian said his business had expanded to Beijing, Changchun and Jilin , where parents were turning to him in the hope of cutting costs by buying from vendors close to Hong Kong. On the mainland's major auction websites, Chinese people in Australia, Japan, the Netherlands and the US offered to send milk powder to parents for 12 yuan per tin. Food processors were also flying off the shelves as parents headed to supermarkets for the ingredients and equipment to make their own infant food. Sichuan mother Zhang Haiyan said she had stopped feeding her eight-month-old daughter domestic baby food since the scandal. She decided to make her own rice and vegetable porridge.