The milk that caused food poisoning in almost 100 middle and primary school children in northwest China contained excessive amounts of E.coli and other bacteria, health authorities announced Wednesday.

Samples of the milk that had been drunk in schools in Xunyang County, Shaanxi Province, were tested and found to have a bacterium density of 16,400 per gram of milk, far exceeding the limit of 10 in per gram, said Zhang Jiman, director of a laboratory of the county disease control center.

Tests of 100 ml of milk also found 230 E.Coli bacteria per gram, while the safe limit was three, said Zhang.

About 100 middle and primary school students started to vomit and had stomach aches after drinking school breakfast milk Monday. Twenty were treated with intravenous drips, said Zhang.

Most of the students had been discharged from hospital, but eight remained for further medical observation, he said.

The milk was delivered to the schools by Baoji-based Shaanxi Renrengao Dairy Co., Ltd., a large milk processor and supplier in the province.

Similar milk food poisoning cases were also reported in Shaanxi's Mian County Monday, where more than 100 students showed the same symptoms and 27 were hospitalized after drinking milk supplied by the same producer.

All of the hospitalized children in Mian County have been discharged from hospital.

Quality inspection authorities in the two counties have sealed off its products for further investigation.