Rescue crews are still sorting through the remnants of collapsed buildings after the deadliest earthquake to strike Mexico City in decades. At least 223 people died in the 7.1-magnitude quake that struck outside Mexico City on the 32nd anniversary of the 1985 earthquake that killed thousands.

Buildings across the city were reduced to rubble, and many people remain missing. At least 25 people were killed when a portion of a three-story school collapsed, trapping students and teachers. One child was found alive.

The earthquake is the third major natural disaster to hit the country in two weeks. Hurricane Katia dumped rain on the country's Gulf Coast on Sept. 8, killing at least two people and leaving thousands without power. The same day, a powerful 8.1-magnitude earthquake struck off the country's southern Pacific coast, killing more than 90 people and toppling hundreds of buildings.

The Mexican government and aid groups are struggling to respond to the series of disasters. After Hurricane Harvey left much of Houston underwater, the Mexican government offered to send supplies and personnel to aid in the recovery effort. The country rescinded that offer on Sept. 11, citing the need for resources to deal with its own disasters.

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The White House said Wednesday that President Trump spoke with Mexican President Enrique Pena Nieto by phone to offer his condolences and pledge to help in the recovery.

"The President offered assistance and search-and-rescue teams, which are being deployed now," the White House said. "The President also pledged to continue close coordination with Mexico as the two countries respond to the recent earthquakes and hurricanes."

The U.S. Agency for International Development (USAID) said Wednesday afternoon that it was deploying a Disaster Assistance Response Team (DART) to Mexico "following a formal request for assistance by the Government of Mexico."

Following the earthquake two weeks ago, Mr. Trump didn't speak to Pena Nieto for six days, angering some Mexican diplomats. State Department spokeswoman Heather Nauert said Tuesday that the U.S. "stand[s] ready to provide assistance should our neighbors request our help."

For those looking to donate to victims and organizations assisting in the relief effort, a spokesman for USAID said the agency recommends donating cash to groups working on the ground. Cash donations are considered the most effective way to help after a natural disaster, since donating material goods can tie up resources need to transport and distribute the supplies.

Here's how to donate to several different organizations working on the ground in Mexico to help victims of the earthquake.

Oxfam Mexico

Ricardo Fuentes-Nieva, the executive director of Oxfam Mexico, tells CBS News that the group's first priority is assisting in the search and recovery efforts to find people who may still be alive under trapped buildings. He said finding housing for those who can't return to damaged structures will be the second phase of the group's response.

Rescue workers and people carry donations of bottled water and food on Wed., Sept. 20, 2017, after an earthquake shook Mexico City the day before. Reuters

"People are responding, self-organizing, working with authorities, contributing to the rescue efforts," Fuentes-Nieva said. "The Mexican people are taking control of the recovery. It's one of the most inspiring things you can see."

Fuentes-Nieva emphasized that the situation in the states of Chiapas and Oaxaca remains dire two weeks after the 8.1-magnitude quake. He said the response on the ground has been disorganized and people are still in need of assistance.

He also said the states closer to the epicenter outside Mexico City shouldn't be forgotten.

"The neighboring states are suffering dramatically," Fuentes-Nieva said. "We need to make sure that Mexico City does not get all the attention."

Oxfam Mexico has launched a fund dedicated to the earthquake response, which can be found here. Oxfam America is also accepting donations for the effort here.

Mexican Red Cross

The Mexican Red Cross deployed 90 ambulances and a rescue unit in the immediate aftermath of Tuesday's earthquake, helping to search for survivors and treating the injured. The organization says it has dozens of doctors and nurses assisting in the effort, and more than 500 volunteers and staff members were working in the hours after the quake.

Red Cross workers walk next to buildings demolished by a 7.1-magnitude earthquake, in Jojutla, Morelos state, Mexico, on Wed., Sept. 20, 2017. AP

The group says 17 rescue and logistics units will arrive on the scene today with an additional 70 staff and volunteers.

"The Mexican Red Cross has extraordinary capacity as it responds to two major earthquakes less than two weeks apart and tropical storms Lidia and Katia, which hit in early September," said Pascale Meige, director of disaster and crisis response at the International Federation of the Red Cross (IFRC). "Hundreds of Red Cross paramedics are out there right now trying to save lives in what is always a race against time."

You can donate to the Mexican Red Cross' earthquake relief efforts here.

Save the Children

Save the Children says it has workers on the ground in Mexico City to assist in the response, with particular concern focused on as many as 100 school children who could be trapped under rubble, the group says.

"Every once in awhile authorities ask for silence so they can hear the people who are still trapped," Save the Children Mexico's programs coordinator Hanna Monsivais said in a statement. "It's amazing what people are doing for others -- but some people are clearly still in complete shock."

The group's director of operations said all staff are safe and accounted for. The group is now focused on protecting children, including the establishment of a "child friendly space" where kids can play and read.

"Children are often the most vulnerable in emergencies such as this and we are particularly concerned because schools across the region were in session and filled with students," Jorge Vidal said.

You can donate to Save the Children here.