The effort to find 12 boys and their football coach who have been missing in a cave in Thailand for a week has picked up pace.

A break in the rain eased flooding in the system of caverns as more experts from around the world joined the mission.

The search effort in the northern province of Chiang Rai has been going slowly, largely because flooding has blocked rescuers from going through chambers to get deeper into the cave.

Pumping out water has not solved the problem, so greater effort has been made to find shafts on the outside of the cave that might serve as a back door to the blocked-off areas where the missing may be sheltering.

Australian police and military personnel were deployed on Saturday to join other multinational teams of experts.

The boys, aged 11 to 16, and their 25-year-old coach entered the sprawling Tham Luang Nang Non cave after a soccer game on June 23, but near-constant rain has thwarted the search for them. Authorities have nevertheless expressed hope that the group has found a dry place within the cave to wait, and that they are still alive.

Reflecting that hope, a medical evacuation drill was held on Saturday morning to see how long it would take to get rescued people out of the cave, into 13 ambulances and to the nearest hospital.

China has sent a six-person team of rescue and disaster experts to the cave, the Chinese Embassy in Bangkok announced on Friday. The group has experience in life-saving rescues in Burma and Nepal, the embassy's statement said.

A second, private Chinese group, calling itself Green Boat Emergency, arrived on Saturday.

"Our skills are search and rescue on mountains and in caves. We hope we can help," said Wang Xudong, a member of the group.

Chiang Rai Governor Narongsak Osatanakorn said the falling water level in the cave has helped the rescue effort considerably.

"Today the situation is much better and we have high hopes, and will be here all night," he said.

Thai navy Seal divers have been crucial to the search, but have been thwarted by muddy water reaching the cave's ceiling, forcing them to suspend operations again and again.

With water levels dropping, they resumed dives on Saturday, re-entering a chamber from which they had retreated earlier in the week.

In addition to pumping out the flooded chambers, there have been efforts to find the source of the water flooding the cave in order to drain or divert it.

Chaiwat Dusadeepanich, of the Department of Groundwater Resources, said his team, which has been drilling for two days, had found a small underground water source near the cave.

"But the water flow rate isn't great enough," he said. "We would have to drill in deeper to get to the source, but at least we found it. Hopefully we can start pumping out the well water by the end of today."

Hopes were also high for finding some kind of access through fissures on the mountainside that might lead to shafts into the cave.

"Yesterday our team climbed into one shaft, and went in around 50 meters (yards)," said National Deputy Police Chief Wirachai Songmetta. He said the shaft had led to two separate chambers so far.

"Today we will re-enter the second chamber that we found and try to find passages that could lead to other chambers."

Officials said on Friday that they were dropping care packages into the shafts in the hope that the missing group might retrieve them.

Each package contains food, beverages, a phone, a flashlight, candles, a lighter and a map of the cave.