In the aftermath of a suspected chemical attack in rebel-held Khan Sheikhoun, in Idlib in north-west Syria, people were choking, struggling to breathe, and convulsing in the street.
Experts say they're all symptoms of nerve agent poisoning.
An ambulance driver gave this account: "Around 6.45 this morning we got news of air strikes in Khan Sheikhoun. We sent three ambulances and it took around 45 minutes to get there. There were still many people suffering from suffocation, mainly children, but also men and women too. Mostly hospitals around the area are full of people suffering from suffocation. It's hard to find the words to describe it, most of those suffering from suffocation are children. More than 50 per cent are children."
The government of President Bashar al-Assad has been accused of being behind the attack.
They deny involvement but the attack came from the air, and the rebels don't have an air force.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
Syrian government MP Fares Shehabi jumped to his government's defence.
"Nonsense. As usual, because we are used to these fabrications and fake news, it's been six years now. We don't need to use chemical attacks. Actually we gave up our chemical arsenal two years or three years ago. We have enough destruction power to fire any place we attack, we don't need to use chemical weapons."
This is the deadliest chemical attack since a sarin gas attack killed hundreds of people in August 2013 in Ghouta, near Damascus.
In the aftermath of that attack, the Organisation for the Prohibition of Chemical Weapons (OPCW) brokered negotiations led by the United States and Russia, which ostensibly saw Syria's stash of chemical weapons destroyed.
One of the first agencies on the ground in Khan Sheikhoun was the Union of Medical Care and Relief Organisations.
Three of their members are in intensive care in an Idlib hospital.
A spokesman, who didn't want to be named, said as many as 500 people may be injured.
He described the attack to Al Jazeera.
"This attack happened in two waves, one wave happened at 6 o'clock in the morning and the other at 2pm, where Rahma Hospital and Sheikhoun Hospital was attacked with chemical agents."
There were doubts whether, after the 2013 attack, Syria had turned over its entire arsenal of chemical weapons; it's suspected they kept up to 200 tons of sarin gas.
In May 2015 the OPCW announced that inspectors had found traces of sarin at a military research site that hadn't been declared by the Assad government.
White House spokesman Sean Spicer, while condemning the attack on US President Donald Trump's behalf, also blamed former President Barack Obama's administration.
"Today's chemical attack in Syria against innocent people including women and children is reprehensible and cannot be ignored by the civilised world. These heinous actions by the Bashar al-Assad regime are a consequence of the Obama administration's weakness and irresolution. President Obama said in 2012 that he would establish a 'red line' against the use of chemical weapons, and then did nothing."
The UN Security Council has scheduled an emergency meeting.
The attack came on the eve of a major international donors' conference in Brussels on the future of Syria and the region.
European Union foreign policy chief Federica Mogherini says it's vital whoever is found responsible is held to account.
"Chemical weapons is the worst of the war crimes. Whoever is responsible for that must be held accountable. We have talked about that with representatives of Syria society, and not one single of them avoids to mention the need to work on accountability and responsibility. If I can pass a message that we share with them, it's that impunity is not an option, especially in front of these terrible scenes we're seeing today."
