Children of migrant workers left in villages nationwide are at serious risk of physical and psychological dangers, mental health professionals have warned following the tragic deaths of five children.

About 58 million left-behind children live in the Chinese countryside, according to a survey by the All-China Women's Federation in 2008.

The number is almost three times of what was recorded in the government's 2000 census.

The rise has been attributed to the vast number of parents who have flocked to cities in search of better salaries, leaving their offspring in the care of older relatives.

Yet, as their numbers have increased, so too has concern over poor educational standards and their general safety, particularly during the summer months.

The latest event to highlight the problems occurred in Anhui province in June when five children were killed while playing in the Shahe River, a 200-meter-long branch of Huaihe River.

Chen Yanhuai, 15, his two cousins, 12-year-old Chen Jian and Yue Cuiwei, had just finished their final exam on June 29 and went for a swim near their homes in Chenjia, a village of about 800 households in the city of Fuyang.

However, they quickly got into trouble, prompting two friends, Chen Yanzhen and Chen Huanhuan, to dive in to help. All of them drowned.

"They were playing on the riverside at first but then decided to swim into the middle of the river where there is a steep slope," said a 10-year-old boy who witnessed the accident.

The parents of the four boys are all migrant workers who were away at the time of the accident.

"Almost all of the parents of children in the village work in large cities to get better incomes," said villager Chen Weigao, 63. "Most of the kids are taken care of by their grandparents."

For 13 years, Chen Weizhou, 57, and his 53-year-old wife have been the only ones taking care of Chen Yanhuai, Chen Jian and Yue Cuiwei.

"For me, that day was the end of the world," said the devastated grandfather, who when interviewed by China Daily reporters simply kept repeating: "I feel so sorry for my sons and daughters. I was supposed to take good care of their children but I did a bad job."

At least 17 youngsters drowned in rivers, lakes and streams across Anhui between June and July, according to figures released by the Anhui education bureau. Most victims were left-behind children in rural areas.

"Sometimes we try to catch spiral shells near the river in summer," said a 10-year-old boy who lives beside Shahe River, "but no one has come near here to play since the accident."