GEOFF BENNETT: In Colombia tonight, the desperate search for survivors is entering a critical phase after the powerful earthquake that devastated parts of that country.

More than 180 people have died, but, 24 hours after the quake struck, there are still remarkable moments of hope.

In Colombia today, neighbors and rescue workers gathered shoulder to shoulder, clearing away mountains of rubble in the search for survivors.

In Santiago de Cali, where dozens of homes and buildings have collapsed, at least 86 people have been pulled from the wreckage, among them this 6-month-old baby and the child's mother.

Rescuers say they heard the mother's cries beneath the rubble and then dug through the debris of their five-story apartment building to reach them.

More than 3,000 people remain missing after the 7.4-magnitude earthquake.

In Pereira, roughly 50 miles from the quake's epicenter, Jairo Vargas joined the search.

The architect says he traveled hours to reach his brother's apartment, convinced he's trapped inside.

JAIRO VARGAS, Searching For Brother (through translator): I'm absolutely certain he's here, absolutely certain.

His horse saddle and all his belongings are here.

He's not answering his phone.

The doorman didn't report him leaving, and his car is parked right there.

And he's not out.

He's got to be there trapped.

GEOFF BENNETT: Pereira is among the hardest-hit areas, where entire residential blocks have collapsed into piles of concrete and twisted steel.

But rescuers say there is still a critical window to find people alive.

JOSE FERNANDO USMA, Red Cross Rescuer (through translator): We still have a big window, about 24 more hours, of which there is hope of finding survivors.

Our biggest advantage is that there may be isolated air pockets or survivable spaces that can allow people to stay alive for a longer period of time.

GEOFF BENNETT: Colombia is mobilizing resources for a massive rescue and recovery effort.

Soldiers who just a day earlier were forced to stop training and brace themselves as the ground shook are now being deployed to help with rescue and cleanup operations.

But reaching the hardest-hit areas itself is a challenge.

Colombia's aviation authorities have closed six airports because of structural damage, potentially complicating the delivery of aid for weeks.

EDWARD DE BURGH, Senior Global Security Officer, Project HOPE: It was a very, very strong earthquake, much more than people had ever experienced before, and we live in an earthquake zone.

GEOFF BENNETT: Edward de Burgh is the senior officer of global security for Project HOPE, a humanitarian organization responding to disasters around the world.

He's based in Bogota.

And he says the quake has damaged the very infrastructure communities will rely on in the weeks and months ahead.

EDWARD DE BURGH: When a disaster of this magnitude happens, when it comes to things like primary health care, hospitals, clinics, which are housed in buildings, are affected like any other building.

Whether they're affected in a dramatic way or even just a way that makes safety an issue for entering them, they tend to close down, and then infrastructure or primary health infrastructure becomes challenged.

GEOFF BENNETT: Back in Santiago de Cali, another search unfolded in agonizing fits and starts.

At even the faintest hint of sound beneath the rubble, rescuers stopped everything and listened.

Overnight, that persistence paid off.

Nearly 24 hours after the quake first shook the country, firefighters found a 35-year-old man trapped under the rubble.

The city's mayor said the man suffered only minor injuries, one rescue offering hope to thousands of families still waiting for word.