Mexico waited anxiously Thursday for signs of life at a collapsed school in the capital, as rescuers continued clawing through rubble for survivors of a 7.1-magnitude earthquake that killed at least 233 people.
Firefighters, police, soldiers and volunteers worked frantically to remove debris in scenes repeated across a swath of central states in Mexico's second killer earthquake this month.
The most agonizing search was at a school in the south of Mexico City where 21 children -- aged between seven and 13 -- and five adults were crushed to death. Many children were still missing.
Rescue workers were desperately trying to reach several children believed to be alive beneath the wreckage in the early hours of Thursday -- more than 40 hours after the quake struck. Using a thermal scanner, they had located signs of life in several locations.
"We know that there is a child alive inside (the destroyed school), what we do not know is how to reach her... without risking a collapse and putting rescuers in danger," rescue coordinator Jose Luis Vergara told Televisa about a young girl whose fate is being closely followed by the country.
A civilian volunteer -- a slight man -- was able to squeeze into a narrow channel through the rubble to reach the girl and pass her water and oxygen.
"I'm very tired," she said, according to the military.
So far, 11 children and at least one teacher have been rescued from the rubble of the Enrique Rebsamen elementary and middle school.
"No one can possibly imagine the pain I'm in right now," said one mother, Adriana Fargo, who was standing outside what remained of the school waiting for news of her seven-year-old daughter.
In the Condesa neighborhood, Karen Guzman sat on a stool in the street with her back to one of the collapsed buildings. She said she could not bear the tension of the search for around 30 people thought to be under the rubble, among them her brother.
Beside her were two street poles tagged with lists of rescued people, but they did not include the name of her brother Juan Antonio, a 43-year-old accountant who worked on the top floor of the four-story building.
"My mom is looking for him in hospitals because we don't trust those lists. Sometimes I think nobody knows anything," she said.
- 50 rescued -
Emergency workers reported that some victims had been rescued thanks to WhatsApp messages they sent to relatives while trapped under the debris.
Rescue teams were helped by thousands of ordinary civilians who dug through the rubble alongside them. Other Mexicans took to the streets with food and water for victims and emergency workers.
President Enrique Pena Nieto toured the hardest-hit areas and declared three days of national mourning.
"The priority remains saving lives," he said in a national address, insisting there was still hope of pulling survivors from the rubble.
More than 50 people have been rescued from collapsed buildings in the capital, he said.
Mexico City Mayor Miguel Angel Mancera told Televisa TV that 39 buildings in the capital had fallen. Searches were under way in all but five where rescuers had determined that nobody remained trapped, he said.
Taiwan confirmed one of its citizens was known to have died, while three others were still trapped. One Taiwanese woman was earlier pulled to safety.
- Nowhere to go -
Many residents spent a second night in parks and plazas, in tents or makeshift shelters, unable or unwilling to return to their homes as authorities inspected some 600 buildings whose walls swayed and cracked when the quake struck.
US President Donald Trump called Pena Nieto and offered assistance and search-and-rescue teams which are now being deployed, the White House said.
Chile and El Salvador pledged aid and Honduras sent 36 rescue workers. An Israeli team of 71 soldiers including engineers and search and rescue specialists was on the ground.
The earthquake hit on the anniversary of a huge quake in 1985 that killed more than 10,000 people, the disaster-prone country's deadliest ever.
Tuesday's struck just two hours after Mexico held a national earthquake drill, as it does every September 19 to remember the 1985 disaster.
A system of quake sensors was set up in 1993 along the Pacific coast, where tremors are more common. People in Mexico City were not warned by it on Tuesday because the epicenter was only 120 kilometers (75 miles) outside the capital and thus outside the main area of sensor coverage, said Carlos Valdes of the National Center for Disaster Prevention.
Adding to the national sense of vulnerability, the earthquake struck just 12 days after another quake that killed nearly 100 people in southern Mexico.
Experts said the two quakes did not appear to be related, as their epicenters were far apart.
Mexico sits atop five tectonic plates, making it particularly vulnerable to earthquakes.
Luis Felipe Puente, the national disaster response agency chief, said that of the dead, 102 were in Mexico City, 69 in Morelos, 43 in Puebla, 13 in Mexico state, five in Guerrero and one in Oaxaca.
In Puebla, a picturesque colonial city near the quake's epicenter, several churches were damaged and one collapsed, killing 11 people attending a baptism, officials said.