Chinese authorities have seized more than 100 tonnes of contaminated milk powder in the north of the country, in a return of the food safety problems that first surfaced two years ago.

A total of 103 tonnes of milk powder from four dairy brands in Hebei, Shanxi and Tianjin were found to be laced with the industrial chemical melamine, the Xinhua News Agency said.

A total of 41 suspects have so far been detained in relation to the case.

In July, samples of milk powder found in northwestern provinces Gansu and Qinghai were found to have up to 500 times over the permitted amount of melamine.

Since then, more than 124 tonnes of the milk powder have been seized in Qinghai and six people have been arrested, Xinhua said.

In 2008, melamine in Chinese milk powder caused the deaths of at least six children and made nearly 300,000 children ill.

Factories have been adding melamine to give their milk powder misleadingly high protein levels so as to pass government inspections.