KUNMING, April 26 -- An initial investigation has found that six schoolboys drowned in a lake in southwest China's Yunnan Province on Thursday, local authorities said on Saturday.

Police in Tonghai County received reports at around 6:40 p.m. on Thursday that seven children had fallen into Qilu Lake. One student was rescued but six others drowned, said Tonghai county government.

An initial investigation found that the seven boys, all of the 6th grade at Dashu Primary School in the county, went to play nearby the lake after school.

At around 5 p.m., some of them boarded a deserted boat, while others were nearby standing on a foam plank floating on the water.

Water entered the boat through cracks. The boat turned on its side, with the boys trying to get rid of water using their shoes.

The boys on the plank and in the boat fell into the lake. One boy struggled to get onto the foam plank.

Haitong county government has started a further investigation into the incident. It also ordered local schools to step up safety education among children and started all-round safety checks to avoid similar accidents.