Photo: The Canadian Press

Residents of the Syrian town of Douma were packed into underground shelters amid bombardment when the gas began to spread. Suddenly, panic ensued.

As shouts of "chlorine, chlorine!" rang out, some ran into the night and fainted in the street. Others climbed to rooftops, hoping they'd be safer rising above the gas. Dozens didn't make it out at all, some stumbling on stairwells, out of breath, where they were later found dead.

The bodies were still there the next morning, strewn around the buildings, including toddlers and young children.

Much about the April 7 suspected chemical attack in Douma, just east of Damascus, remains unknown, including the exact death toll, because of the lack of an independent investigation.

International chemical weapons inspectors were said to have entered the town on Tuesday, 10 days after the attack, but the Syrian government said Wednesday that only an advance security team had entered, amid U.S. accusations that Syria and its ally Russia were blocking their entry to cover up evidence.

The Associated Press spoke to rescuers, medics and numerous residents of Douma for their accounts of what took place. Some were reached in rebel-held areas in northern Syria where they were evacuated after the attack, while others were still in Douma.

They spoke of at least two buildings with people sheltering in the basements that were overwhelmed with gas so strong that it was hard to breathe hundreds of meters (yards) away.

More than 40 people were killed, many of them children, according to medics and opposition activists in the town. The World Health Organization said an estimated 500 patients exhibited symptoms consistent with exposure to toxic chemicals, including respiratory failure.

It was hardly the first chemical attack in Syria's civil war, now more than seven years old. The U.N.-mandated Independent International Commission on Syria has documented more than 30 chemical attacks in Syria between 2013 and the end of 2017 — at least 25 of them carried out by the Syrian military, the commission says. For the rest, it had insufficient evidence to determine the perpetrator. Most involved chlorine gas, usually causing only a few injuries.

But in this case, it appeared the gas hit dozens of people crammed into confined spaces, huddling away from the bombs outside. The U.S. and France say they have evidence the Syrian government carried out the April 7 strike, while Syria and Russia have denied any gas attack even took place.

An AP team visited the site on a Syrian government-organized tour Monday, including a two-room underground shelter where one resident said 47 people were killed, including his pregnant wife and two young daughters.

A strange smell lingered, nine days after the attack. The floors of the shelter were covered with carpets and pillows were lined up against a wall. There were no signs of blood stains.