Rescuers search for survivors at the Enrique Rebsamen school after an earthquake in Mexico City, capital of Mexico, on Sept. 20, 2017. Elements from the civil protection corps, Red Cross, army, police and voluntary civilians worked through the day on Wednesday to remove rubble from collapsed buildings in Mexico City, after the magnitude-7.1 earthquake shook the center of the country on Tuesday. (Xinhua/David de la Paz)

President Xi Jinping sent a condolence message to Mexican President Enrique Pena Nieto on Wednesday over the magnitude 7.1 earthquake that killed at least 237 people and injured more than 1,900 in south-central Mexico this week.

Xi also extended deep sympathy to the Mexican people, profound condolences to the victims and sincere concern to relatives of the victims and those who were injured.

Xi said he believes that under Pena Nieto's leadership, the Mexican people will overcome the disaster and rebuild their homes.

China is willing to help with Mexico's relief and reconstruction efforts, Xi added.

On Thursday, as the odds of survival diminished with each passing hour, rescuers continued to claw through rubble for survivors.

Throughout the capital, crews were joined by volunteers and bystanders. Rescuers used dogs, cameras, motion detectors and heat-seeking equipment to find victims who might still be alive.

So far, more than 50 people have been plucked from several disaster sites, leading to impassioned choruses of "Yes we can!" from the first responders, volunteers and spectators near the ruins.

The most agonizing search was at a collapsed school in southern Mexico City, where Navy-led rescuers could communicate with trapped a 12-year-old girl and continued to work toward freeing her.

Rescuers had seen a hand protruding from the debris and the girl wiggled her fingers when asked if she was still alive, according to broadcaster Televisa.

But some 15 hours into the effort, Admiral Jose Luis Vergara said rescuers were still unable to reach her.

"There's a girl alive in there, we're pretty sure of that, but we still don't know how to get to her," Vergara said.

The earthquake struck about 150 kilometers southeast of Mexico City on Tuesday afternoon, shattering glass, shearing off sides of buildings and leaving others in dusty piles of destruction.

It came on the same date as a 1985 tremor that killed thousands and still resonates in Mexico. Annual Sept 19 earthquake drills were being held a few hours before the nation got rocked once again.

At least nine Latin American countries have pledged to rush in search-and-rescue teams or technical assistance, with crews from Panama and El Salvador already on the job. The United States, Spain, Japan and Israel also pledged help.