The Taliban claimed responsibility for the blast, a week after it claimed an attack on the Intercontinental Hotel in Kabul in which more than 20 people were killed.
"It is a massacre," said Dejan Panic coordinator in Afghanistan for the Italian aid group Emergency, which runs a nearby trauma hospital. In a message on Twitter, the group said more than 50 wounded had been brought in to that hospital alone.
A spokesman from the public health ministry said 17 dead and 110 wounded had been brought to city hospitals, and victims were still being brought in.
Mirwais Yasini, a member of parliament who was nearby when the explosion occurred, said the ambulance approached the checkpoint, close to an office of the High Peace Council and several foreign embassies, and blew up.
A plume of grey smoke rose from the blast area in the city centre and buildings hundreds of metres away were shaken by the force of the explosion.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)