(BSS/AFP) - Colombia`s earthquake rescue efforts entered what officials called the "final phase" on Wednesday, as rescuers searched for signs of life beneath collapsed buildings before the critical first 72 hours came to an end.

The magnitude 7.4 quake, the strongest to hit Colombia this century, has killed 265 people, injured more than 3,500 and left almost 500 missing, according to local authorities.

In the city of Pereira, crews focused on a collapsed bakery where they believe a street vendor trapped since Monday`s earthquake may still be alive beneath the rubble.

Using equipment that detects vibrations, rescuers said they had picked up possible signs of life from Pablo Loaiza, prompting anxious relatives to gather outside the wreckage.

"They tell us it could be him," said 16-year-old Sara Loaiza, his niece. "My heart is about to burst out of my chest," she cried.

Relatives said the trapped man appeared to respond when rescuers asked him to knock twice, then three times from beneath the rubble, drawing applause from those gathered at the scene.

Crews are approaching 72 hours since the quake, a period when survivors are considered most likely to be found alive beneath collapsed buildings.

"We`re entering the final phase," Cali Mayor Alejandro Eder said Wednesday. "That doesn`t mean there won`t be survivors afterwards, but it is more difficult."

In Cali and Pereira, emergency crews prepared to work through a third night with their bare hands, cranes and sniffer dogs, stopping not to rest, but to listen for signs of life.

"Every half hour we make everyone be quiet to see if we can find people alive," volunteer rescuer Johana Sanchez told AFP.

"So far, three people have been pulled out alive and three dead."

Colombia`s newly installed president has declared the disaster an "economic emergency" and announced three days of national mourning.

"We will do what is necessary," Abelardo de la Espriella said in a statement, vowing to "emerge again as a country and as a society."

According to official figures, more than 11,000 dwellings have been destroyed and thousands of families have been rendered homeless.

Many have already spent consecutive nights outdoors, either because their homes were damaged or because they feared aftershocks.

In the mountain town of El Cairo, residents gathered at community kitchens Tuesday while power outages persisted and many remained reluctant to return home.

"People don`t want to go inside their homes, people don`t want to sleep, people don`t know what to do," resident Adriana Gonzalez told AFP.

In nearby Roldanillo, Yuliana Mendez picked through the wreckage of the beauty products store where she worked, one of many businesses damaged in the disaster.

"It`s like starting over from scratch," she said.

Bringing water, donating blood -

In Pereira`s Providencia neighborhood, residents hauled furniture and household items from damaged buildings. Among them was lawyer Ana Paulina Crosthwaite, whose apartment block was left unsafe by the quake.

"We`re in a state of shock," she told AFP. "We`re not prepared to tell our children that we have to pack whatever we can and start a new life."

Many Colombians have mobilized to help, bringing water, food and supplies to affected neighborhoods, while long lines formed outside blood donation centers.

"It`s about wanting to help your community, your city and your country," said blood donor Ferney Cabrera.