Beijing reported its first mass infection of the H1N1 flu at a primary school Wednesday.

Seven pupils between 8 and 10 years old were confirmed infected with the virus Tuesday night, according to a press conference held last night.

The pupils, mainly second and third graders, are all with the Nanhuzhongyuan Primary School of Chaoyang district. The school has 841 pupils and 78 staff.

Fang Laiying, chief of the Beijing municipal health bureau, said the seven students are now in stable condition in hospital.

Another four pupils who had fever on Tuesday are still undergoing further tests.

A total of 154 others - 93 students, 20 teachers and 41 family members of students - are quarantined, Fang said.

The rest of the 700-odd students and faculty members of the school are required to stay quarantined at home for seven days.

Zheng E, deputy chief of Beijing municipal commission of education, said the school started summer vacation Wednesday, one week ahead of schedule.

"It will then start school a week earlier than other local schools, and final exams scheduled for this week will be postponed to after the summer break," Zheng said.

As the school is located in a populous neighbourhood, health authorities were highly concerned about the situation and epidemiologists are tracking the source of the outbreak.

On Monday, 18 students from four Grade 2 and 3 classes at the school were absent with 12 running a fever, according to school authorities. Seven of them tested positive for the H1N1 virus on Tuesday.

The capital health department called for tight prevention and control measures among students before summer vacation.

An emergency meeting of education committees of Beijing's 18 districts and counties was held Wednesday to intensify the prevention of the pandemic among students, especially at major events held during summer vacation.

As of Wednesday, the mainland has reported 867 confirmed cases, with 155 in Beijing.