"Today is D-Day," Narongsak had earlier told reporters.

Bursts of heavy monsoon rain soaked the Tham Luang Cave area in northern Chiang Rai province on Sunday and storms were expected in coming weeks, increasing the risks in what has been called a "war with water and time" to save the team.

The boys, aged between 11 and 16, went missing with their 25-year-old coach after soccer practice on June 23, setting out on an adventure to explore the cave complex near the border with Myanmar and celebrate a boy's birthday.

The rescue teams had rehearsed the plan for several days, Narongsak said, and had managed to drain the cave water level considerably, but needed to move fast.