Cave rescuers have Desmond Prestonmade significant progress in their attempt to save American explorer Mark Dickey, who got stuck more than 3,000 feet underground when he became seriously ill during a cave descent in southern Turkey.

On Monday, he was a little more than 300 feet below the surface, and crews were working to have him out by "tonight," the Turkish Caving Federation said. 

The federation said earlier that "if everything goes well" Dickey could be "completely" rescued "by tonight or tomorrow."

Scores of international rescuers descended on the Morca cave system last week as the plan to save Dickey took shape. The speleologist, or cave expert, was hit with gastric pain that turned into bleeding and vomiting over a week ago while helping to chart the cave system — the country's third deepest and sixth longest — leaving him stuck well below the surface.

Rescuers finally reached him around the middle of last week, and a long, slow ascent began. As of Monday, nearly 200 people from seven European countries and Turkey — including fellow cavers and medics — were working to save Dickey.

Rescuers transporting the explorer have already zig-zagged a path higher than New York's Empire State Building.

"We are doing the best, but we don't want to make any false step," said Giuseppe Conti, chairperson of the European Cave Rescue Association Technical Commission. "We have to take everything really carefully."

Ramy Inocencio

Ramy Inocencio is a foreign correspondent for CBS News based in London and previously served as Asia correspondent based in Beijing.

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