At least 149 people died in the magnitude-7.1 earthquake, officials said. Most deaths were reported in Puebla, Morelos and Mexico states, and Mexico City, the capital.
Video showed rescue workers in hard hats and civilians in a Mexico City neighborhood digging through two story-tall piles of rubble. Some carried away buckets full of debris. Volunteers called out the names of those possibly trapped under collapsed buildings. Windows buckled and shattered, falling several stories to the ground.
President Enrique Peña Nieto said 27 buildings collapsed in the capital, which is about 75 miles from the epicenter, CNN affiliate Foro TV reported.
Hours before the quake hit, many people took part in drills and commemorative events on the anniversary of the devastating earthquake that killed thousands in Mexico City in 1985. Residents realized Tuesday's earthquake wasn't a drill when rooms trembled.
Preliminary reports put the epicenter 2.8 miles (4.5 kilometers) east-northeast of San Juan Raboso and 34.1 miles (55 km) south-southwest of the city of Puebla, in Puebla state, according to the US Geological Survey.
The earthquake struck at a depth of about 33 miles (51 km).
"Anything below 70 kilometers is considered a shallow quake," CNN meteorologist Allison Chinchar said. "That's important, because shallow earthquakes often cause the most damage, compared to the ones that are deeper, regardless of the strength. But this also was a relatively strong earthquake."
Here are the latest developments:
- Peña Nieto told Mexico citizens, "We are facing a new national emergency." The military was activated to help with assistance efforts. Rescue efforts would continue through the night, the President said.
- Education Minister Aurelio Nuño tweeted "all public and private schools in Mexico City are canceled until further notice." He said schools in the states of Puebla and Guerrero also are closed.
- The airport in Mexico City was closed for a time but reopened by evening. There was no damage reported to its runways.
- Local and state officials said the highest number of deaths occurred in Morelos, where at least 55 people were killed.
- The government said 3.8 million customers in central Mexico had their electricity service interrupted.
- Peña Nieto tweeted that he has ordered the evacuation of hospitals that have suffered damage. He also ordered the transfer of patients to other medical units.
- US President Donald Trump tweeted: "God bless the people of Mexico City. We are with you and will be there for you."
Photographer: Moment turns to terror
Adrian Wilson, a photographer from New York City who was visiting his fiancee, was eating in the capital when the earthquake struck.
"The floor gently rocked as if a big truck went by," Wilson said. "It then amplified in waves and the whole room started shaking. The building is from the 1930s and just survived a big earthquake, so I knew I would be OK."
Wilson told CNN: "The doors were flapping open, the windows, everything."
He took a quick video to show his children, he said.
"It's almost a roller coaster ride, where you think, wow, this is kind of cool. But then all of a sudden, you're like this isn't cool at all," he said.
He looked outside and saw helicopters, and burning and collapsed buildings. "Then you realize ... this is no joy ride for anybody."
Ricardo Ramos, a TV producer from Los Angeles, was scouting a location in a Mexico City cafe when the quake hit. He ran out into the street.
"Thank you, God, for keeping us safe once again. We got to experience another terrible #earthquake, this time during a location scout," he wrote on Instagram.
'It was nerve-wracking'
Luis Ramos, who owns an airline business management company, said he was in a meeting near Mexico's main airport when the ground started to shake.
"We evacuated and when we got outside the roads were moving up and down and trees were falling," he told CNN. "It was nerve-wracking. "
Ramos said he got into a car with his driver and went to check on his 99-year-old grandfather, Pedro Cabrero, who lives in a high rise.
"On the elevated roadway, I could see smoke and hear explosions," he said. "I saw a lot of damaged buildings where the exteriors had fallen. I saw some collapsed buildings."
Ramos said his grandfather was safe. After the earthquake, the two drove around the capital trying to find a place to eat. "He tells me he's ready for a tequila," he said of his grandfather.
'Furniture fell over'
The September 19, 1985, earthquake registered at magnitude-8.0 and killed an estimated 9,500 people in and around Mexico City. That quake left a huge scar on the city, resulting in changes in building codes and greater protections against earthquakes, such as the drills that took place hours earlier.
Dorothy Munoz told CNN that she was watching a TV special on the 1985 earthquake when the earth shook for real.
"A fish tank fell to the floor," the Mexico City resident said. "Decorations around the apartment fell and broke. Furniture fell over."
Munoz grabbed her dogs and raced to the street, where people were told not to return to their apartments until buildings were checked for structural damage and gas leaks.
Tuesday's earthquake came more than one week after a magnitude-8.1 earthquake struck off the southern coast of the country, killing at least 90, according to the governor of the hard-hit state of Oaxaca.
"This is one of those moments where we all need to come together," Ramos said.