Graphic video purporting to show the immediate aftermath of the blast depicted massive plumes of smoke, bodies strewn on the street, and people frantically running for their lives.
The video was posted on a social media website on Sunday.
At least 250 people were wounded in the attack, conducted by President Bashar al-Assad's regime forces, activists say.
"In some places there was not enough capabilities to transfer the victims. It was very painful to see dead human bodies just left on the sidewalk," said Abdullah al-Shami, a media activist, speaking to CNN via Skype. "Scores of injured were bleeding while waiting their turn to get treatment."
Multiple airstrikes hit a busy local vegetable market in Douma, about 15 kilometers (10 miles) northeast of Damascus, causing large-scale casualties, according to the London-based monitoring group Syrian Observatory for Human Rights, along with the Qasioun News Agency, a local media network, and activists inside Douma.
"This market was bombed recently. The ambulance system was on alert but today the ambulances were not even enough to rescue all the people. The number of the injured was over the capabilities of the field hospitals," said al-Shami.
The Syrian Revolution Network
, an online network of activists with more than a million followers, tweeted: "50 markets bombed by Assad regime since the beginning of 2015. This one in #Douma bombed twice in 4 days."
CNN cannot independently verify these accounts.
Syria's state-run news agency SANA, which is pro-al-Assad, has yet to report the incident.
Syria has been locked in a civil war since 2011, after street protests erupted out of the Arab Spring and morphed into a nationwide uprising against the regime. Douma, a major city in the province of Rif Damashq -- meaning Damascus countryside, which includes the suburbs that surround the capital city -- has been consumed by bloodshed since the uprising.
The ongoing violence has become a part of the daily life of many Syrians. Many have grown numb to the warning sirens.
"There are alert sirens but we hear them more than 20 times a day and now they have lost their impact," said al-Shami.
Since the unrest, hundreds of thousands of refugees have fled the country.
In July, the United Nations reported that more than 4 million Syrians had fled the violence in their homeland to seek refuge in neighboring countries.
Antonio Guterres, the U.N. high commissioner for refugees, has called the mass exodus "the biggest refugee population from a single conflict in a generation."
At least 7.6 million other people have been displaced inside Syria, according to the U.N. refugee agency. That means more than half of all Syrians have been driven from their homes by the war, which has killed well over 200,000 people.