Wolf said he had been on site for about 15 hours a day, seven days a week, and that when he first arrived he worked 38 hours straight.

"I spent New Year's Day on night shift," he said.

When the four survivors were finally returned to the surface at about 10 pm on Friday, Wolf said he was happy and excited, and joined in the applause with fellow rescuers.

He is now looking forward to returning home to his family in Germany, although he did not know when that would be.

The German expert said the Chinese government provided good support for the rescue and that he worked well with Chinese colleagues, including the head of the rescue team.

"He's a very good, smart man, and he took the right decisions," Wolf said of the team leader, adding that the experience overall had been a rewarding one. "I'll show everything to my German students. I learned a lot here."

Contact the writers through wangxiaodong@chinadaily.com.cn