Time is running out to find survivors.

A woman was rescued from the rubble of a collapsed building 22 hours after an earthquake leveled parts of Turkey and Syria, the Turkish state news media service Anadolu Agency reported early Tuesday.

More than 16,000 rescuers were engaged in a search effort for survivors, the agency said, citing an emergency management official. But the window for finding others was beginning to narrow, experts said, and the specialists flying to Turkey from the United States and beyond were certain to face challenges gaining access to the site and executing rescue operations.

From one to three days after an earthquake is usually the “golden period” for saving lives, said Lody Korua, a search and rescue expert in Indonesia who has volunteered for earthquake response operations for more than 15 years. Even then, the logistics can be very complicated.

“The people we’re rescuing are injured — they are under rubble, and we don’t know how deep down under,” he said. “They are stuck, maybe with their legs crushed by the collapsed structure, with broken bones, and they can’t cry for help.”

Some survivors have been found four or more days after an earthquake, said David Lewis, who coordinates an international urban search and rescue team for the fire and rescue agency in New South Wales, Australia. He added that the amount of time a person can survive in rubble depends on several variables, including the temperature, their access to food and water and the way in which they were trapped.

Unfortunately, he added, the powerful earthquake that hit Turkey and Syria came in the middle of the night — a time when many people would have been asleep and unable to find a safer place to shelter.

“Then it would just be hoping that when the building collapses,” he said, “there was a void and you didn’t have the roof or the upper story coming down on top of you.”

The effectiveness of the specialists racing to the earthquake zone will depend partly on how well they coordinate and on how quickly they arrive. But the area is remote and relatively hard to gain access to, said Yosuke Okita, an expert on international emergency management at Keio University in Japan.

If small airports in the area do not have capacity to transport search and rescue personnel and their heavy gear, the teams would need to fly to larger airports and travel to the earthquake zone by truck, Mr. Okita said. Finding trucks may also prove difficult, he added, and some roads to the stricken area are blocked.

When they do arrive, the rescuers entering partly collapsed buildings will be working in dangerous environments.

Many of the buildings in the earthquake zone appear to be lightly reinforced concrete and masonry structures that are several decades old, said Jerome F. Hajjar, a structural engineer at Northeastern University who specializes in earthquakes. That means they could be vulnerable to further collapse in the event of a large aftershock, or to a fire caused by a gas leak.

“That just makes the situation all the more challenging,” Professor Hajjar said.