A distraught mother mourned her "perfect" son on Sunday, after he was killed when his school collapsed during tremors in Yunnan province.

Wang Yaoyou, 7, was one of three students crushed to death on Friday when the classroom where they were eating lunch was razed by a violent earthquake.

"He was such a good boy, perfect," said Zhang Congmin, the boy's 41-year-old mother, who also has two daughters.

"He always listened and never made trouble," she said, crying. "I don't know how I will go on in the future."

A 5.7-magnitude earthquake rocked Yiliang county in northeast Yunnan at 11:19 am, followed by a 5.6-magnitude quake about an hour later.

Wang was among seven students, all aged 5 to 7, who were in Yunluo Primary School, a one-building structure.

Zhu Yinquan, principal and the only teacher at the school, said he had been eating lunch at a friend's home nearby.

"I felt the tremor and I remembered there were seven students in the classroom," said the 34-year-old. He immediately ran back to the school.

When Zhu arrived he saw the classroom had been reduced to rubble.

He and several other villagers dug three bodies out of the wreckage.

Another four students were injured and taken to hospital. Two were discharged on Saturday.

Yunluo Primary School had 22 students, although most had returned to their homes for lunch on the day of the quake.

Zhu, a middle school graduate, started teaching at the school on Wednesday, just two days before the earthquake.

He said the school has suffered a teacher shortage because several teachers moved to cities to work.

According to Beijing News, officials said the classroom was old and shabby, which could be one of the reasons for the collapse.

Yiliang has 357 primary and middle schools, with 118,342 students and 4,914 teachers and staff members.

As of Saturday morning, three students were killed, with 20 more injured in the quake. Two teachers were also injured.

Beijing News quoted Zhou Guangfu, deputy director of Yiliang education bureau, as saying that because of the earthquakes, many school buildings are now unsafe.

Zhou told the paper that all schools in the county have been closed and tents are in heavy demand.

Contact the writers at guoanfei@chinadaily.com.cn and luowangshu@chinadaily.com.cn