Some children died before they reached the hospital; others were asking for their parents as they received treatment.

Doctors in Syria described to ABC News some of the youngest victims they treated after today's chemical attack in northern Syria.

Mizar Hassani, a doctor at a hospital in Idlib, about 30 miles away from Khan Sheikhoun, the town that was hit, said he treated around 30 patients, among them four children.

“They just woke up to find everything in their life changed,” Hassani told ABC News via Skype, adding that the children kept crying.

“When we receive them they are crying … we will give them our medication, our treatment. When they wake up they are crying,” he said, pausing before adding, “I cannot continue ... their father, mother died. What will we do for them?”

A Syrian child receives treatment following a suspected toxic gas attack in Khan Sheikhun, a rebel-held town in the northwestern Syrian Idlib province, on April 4, 2017.(Mohamed al-Bakour/AFP/Getty Images) A Syrian child receives treatment following a suspected toxic gas attack in Khan Sheikhun, a rebel-held town in the northwestern Syrian Idlib province, on April 4, 2017.

The children he treated survived and are doing better now, he said. When the victims of the attack first arrived at the hospital, they were drowsy and agitated and had lesions and runny noses – symptoms consistent with a gas attack, he said.

Abdulhai Tennari, who also treated victims, said the attack happened at 6 a.m. local time. Six hours later children started to arrive at his hospital.

“Children arrived dead,” he told ABC News in a voice recording in Arabic. “They were found under the rubble. There are children who don’t have their parents. We don’t know where their parents are. We treated them and are looking for their parents. Their parents might be looking for them.”

He said many of the injured died on the spot. Others died on their way to the hospital while some survived and were treated. Most of those killed died from choking on gas, he said.

A man carries a child following a suspected chemical attack inside a makeshift hospital in the town of Khan Sheikhoun, northern Idlib province, Syria, April 4, 2017, in a photo provided by the Syrian anti-government activist group Edlib Media Center.(Edlib Media Center, via AP) A man carries a child following a suspected chemical attack inside a makeshift hospital in the town of Khan Sheikhoun, northern Idlib province, Syria, April 4, 2017, in a photo provided by the Syrian anti-government activist group Edlib Media Center.

Many patients were transferred to Turkey because Syrian hospitals were at capacity. At least 72 civilians were killed in the attack, including 20 children, according to the Syrian Observatory for Human Rights. The Syria Civil Defense and the Health Directorate in Idlib said in a statement that more than 50 people were killed and 300 were injured.

“The problem is that it’s a long way from Khan Sheikhoun to us in Idlib and then to Turkey. The patients are in serious condition and might die because of the delay of their treatment,” Tennari said. “I have patients who are still not awake.”

Save the Children said that medics in the area told its staff that nearly a third of the casualties they have seen are children, who are arriving at hospitals pale and unconscious or struggling to breathe.

“Doctors at a health clinic run by our partner Syria Relief told us they received three children under 6 years old today,” Sonia Khush, the Syrian director of Save the Children, said in a statement. “They were struggling to breathe and barely conscious, with running noses and contracted pupils – doctors say these symptoms are consistent with the use of nerve agents such as Sarin."

A Syrian child receives treatment at a small hospital in the town of Maaret al-Noman following a suspected chemical attack in Khan Sheikhun, northwestern Idlib province, Syria, on April 4, 2017.(Mohamed al-Bakour AFP/Getty Images) A Syrian child receives treatment at a small hospital in the town of Maaret al-Noman following a suspected chemical attack in Khan Sheikhun, northwestern Idlib province, Syria, on April 4, 2017.

If a banned chemical substance is confirmed, this would be in clear violation of international law and an indication that not all chemical weapons have been destroyed in Syria, as demanded by the UN Security Council Resolution reached in September 2013, the statement read.

Syria's Foreign Ministry said Damascus is committed to its obligations under the Chemical Weapons Convention it joined in 2013, denying its military has used such agents in today’s attack. In comments to the official news agency SANA, a Foreign Ministry official said the country's military has no chemical weapons of any kind.

The Organization for the Prohibition of Chemical Weapons said in a statement that its fact-finding mission is in the process of gathering and analyzing information from all available sources about the chemical weapons attack.

“The OPCW strongly condemns the use of chemical weapons by anyone, anywhere and under any circumstances,” the organization said in a statement.

The Syrian American Medical Society said its doctors on the ground saw patients with pinpoint pupils, foaming at the mouth, loss of consciousness, slow heart rate, slow breathing, vomiting, muscles spasms and other neurological symptoms consistent with nerve agents.