Rescuers were working Monday to bring out a man stuck deep inside a cave in the German Alps after he was hurt by falling rocks, an effort that officials said would take days as experts negotiate a tricky labyrinth of vertical shafts and bottlenecks.

'We have shafts that go straight down 350 metres, where you have to rappel down and climb back up on a rope.'- Klemens Reindl, mountain rescue official

A four-member rescue team reached the experienced 52-year-old German cave researcher early Monday inside the Riesending cave system, near Berchtesgaden in Germany's southeastern corner.

The man, whose name wasn't released, had suffered head injuries a day earlier. One of his two uninjured companions made a 12-hour climb back to the cave entrance to alert authorities, while the other stayed with him.

The injured man is nearly 1,000 metres below the surface "in one of the most difficult caves in Europe," mountain rescue official Klemens Reindl told n-tv television.

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Rescuers were working Monday to recover a man stuck deep inside a cave in the German Alps after he was injured by falling rocks. The 52-year-old cave researcher could remain in the cave for days, rescuers said. (Associated Press, Bayerisches Rotes Kreuz handout)

Officials said he is around 6,000 metres from the cave entrance. He is believed to be in stable condition.

"We have shafts that go straight down 350 metres, where you have to rappel down and climb back up on a rope," he said. The cave system has tight spots where only a slim person can squeeze through, and explorers also have to contend with water.

Rescuers laid a telephone line several hundred meters deep on Monday to help the rescue effort, while others set up camps inside the cave system on the border with Austria. They were working in small teams of up to four people each.

Another mountain rescue official, Stefan Schneider, told a televised news conference that a doctor was in the cave, but it wasn't clear when he could get to the patient.

"It's going round the clock, and it's going to last a few more days," Schneider said.

Cave rescue specialists from Germany, Austria and Switzerland were involved in the operation.