BERLIN — When the first earthquake began to rattle the family home in southern Turkey, Neslihan Yakili called her sister in Germany.

“It was horrifying,” Fatima Oztirak said. “They had no idea what was going on.”

Oztirak, 36, listened helplessly from the German capital as her loved ones described the disaster back home: Buildings around them were collapsing. They had dashed out to the street. (They’ve slept in a tent there ever since.)

The devastation wrought by the two earthquakes that shook southern Turkey and Syria on Monday has shocked the world. The death toll passed 11,000 on Wednesday, making it the world’s deadliest earthquake in a dozen years.

But few Western countries have closer ties to the hardest-hit regions than Germany, home to the world’s largest Turkish diaspora community, estimated in the millions, and hundreds of thousands of Syrians who fled the country’s civil war.

Many have spent desperate days attempting to contact loved ones. Deutsche Telekom, the country’s largest phone provider, has made calls and messages between the countries free for a week.

In Berlin, businesses have shuttered and the city hall has flown its flags at half-staff. The Bundestag held a moment of silence on Wednesday. Aid centers have sprung up to gather donations.

Oztirak canceled appointments at her beauty salon Wednesday morning so she and her partner could take donations of baby food and diapers to a collection point set up at a Turkish music school in Berlin’s Kreuzberg district. It’s the heart of the city’s Turkish community; some donors were too upset to speak.

“I haven’t slept in days,” Oztirak said. “It’s on your mind the entire time.”

The mountains of donations are posing a logistical challenge for volunteers. By Tuesday, three halls in Berlin’s Neukölln district had already filled up. Mayor Franziska Giffey said she was in touch with Berlin’s -Brandenburg Airport to discuss the possibility of making a hangar available for donations.

“We know that right now, very, very many Berliners with Turkish roots are looking to Turkey with great concern, are deeply shocked, have relatives there, have friends there,” she said. “In these hours we see very, very many people in Berlin collecting donations trying to help.”

Germany doesn’t keep data on ethnicity, so there’s no official count of residents with Turkish heritage. Estimates range from about 3 million to 7 million — as much as about 8 percent of the population.

“We’re trying to do everything we possibly can to help,” said Selma Can, 48, an aid coordinator at the music school.

Like many of the volunteers, she comes from a family that arrived in Berlin at the end of the 1960s. After World War II, West Germany urgently needed laborers to boost production in a booming economy. Hundreds of thousands of these guest workers, many from Turkey and Italy, answered the call. In the years that followed, many brought over their families.

“Everyone’s ready to help,” Can said. “Not just people from the Turkish community, but Germans and other people, too.”

For Can, this week has brought back painful memories of the country’s 1999 quake that caused about 18,000 deaths. She and her family were in Turkey at the time.

“It was such a traumatic experience,” she said. “We lived in a tent for a week.”

As communities rallied on Wednesday, there was growing frustration about the difficulty of getting aid to affected areas of Syria. The war there has left the country divided into separate regions controlled by the government of President Bashar al-Assad, U.S.-backed Kurds and the opposition.

Ali Ertan Toprak, the chairman of the Kurdish Community in Germany, called on Turkey to open the border with Syria so that aid could be delivered quickly to the conflict region.

Chancellor Olaf Scholz told the Bundestag on Wednesday that Berlin was in close contact with the United Nations to deliver aid.

He spoke of the “close connection between our entire society” and those who have lost loved ones, and described the need as “huge.”

At least 800,000 people of Syrian heritage live in Germany, most of them refugees from the war.

Yosra Alahmad lives in Berlin but teaches Arabic and English, virtually, to 40 orphaned children, ages 5 to 17, in a refugee camp in Idlib, Syria. She was planning to gather donations for her students.

For 10 hours after the quakes, she didn’t know whether they were alive or dead. “It was one of the hardest days of my life,” she said.

She finally received the call: Nine of her students were injured, but all survived.

Oztirak said she’d been able to contact all her relatives. “But on my mother’s side, several people have died,” she said.

At the music school, rehearsal rooms had been repurposed to unpack and organize the donations into boxes. A chain of volunteers stretched along a hallway into the parking lot. Rubbing their hands in the below-freezing temperatures Wednesday, they passed labeled boxes to load onto a truck.

As the aid mounted, some centers said they would have to turn away donations.

“We can’t all be there right now, so helping here is the least we can do,” said Bilal Simay, a 27-year-old construction worker at an aid point at the Titanic Chaussee Berlin hotel. A volunteer nearby attached a label printed “battaniye” — blankets — to a sealed box.

Fatih Dogan, a 40-year-old taxi driver, said he’d learned through social media posts that he had lost several friends. As time passes, hope for survivors is fading.

“All the rescuers seem to be pulling out of the rubble is bodies,” he said. “The families of so many friends are just gone. All of them.”

Rosenzweig-Ziff reported from Washington.

previous coverage

• Pentagon positions aircraft carrier to help Turkey’s earthquake recovery efforts
• US and NATO allies in Europe converge on Turkey to aid earthquake recovery