An intricate rescue effort is underway in Germany to save an injured speleologist trapped in a cave 1,000 metres (3,300 feet) below the surface of the earth.

Some 200 emergency personnel are working to bring the 52-year-old out of the Riesending, Germany's deepest cave system near the city of Berchtesgaden on the Bavarian Alps.

The man, named by German media only as Johann W., was hit by falling rocks as he was exploring the cave's deeps with two other researchers over the weekend.

He reportedly suffered from severe injuries to the head and torso which prevented him from climbing back to the entrance of the 19.2 km underground labyrinth of vertical shafts and bottlenecks, described by mountain rescue official Klemens Reindl as "one of the most difficult caves in Europe".

One of his companions remained with him, while it took 12 hours for the other to return to the surface and alert authorities.

The Riesending reaches a maximum depth of 1,148 and the injured man is nearly 1,000 metres underground, police said.

"We have shafts that go straight down 350 meters (1,150 feet), where you have to rappel down and climb back up on a rope," Reindl said.

Germany media described Johann W, as an expert speleologist who was part of the team of researchers who first explored the cave in 2002. Its entrance had only been discovered in 1995.

The mountain rescue service said the cave is particularly difficult to penetrate, as it features spots where only a slim person can squeeze through.

Explorers have also had to contend with water.

Matthias Leyk, who is directing the rescue effort and has known the trapped speleologist for more than 20 years, told Bild newspaper that avoiding contact with water is essential for surviving cold temperatures underground.

Leyk said it can get as cold as 3 Celsius degrees in the cave around this time of the year.

Rescuers working in small teams of up to four people laid a telephone line several hundred metres deep and were setting up camps inside the cave system.

It could take days to reach him and bring him back up, they said.