attack: The “unmanned aerial vehicles” violated South Korean airspace in the border areas around Gyeonggi province, said the country’s joint chiefs of staff.
One drone flew all the way to the northern edge of the capital, Seoul, before returning across the border.
Jets and attack helicopters were deployed, but 100 rounds fired from helicopters failed to shoot them down.
A South Korean military official said they had since lost track of all the drones, but that they were no longer in flight.
The incursion comes amid increased tensions on the Korean peninsula, with the North conducting a record number of missile tests this year.
The drones were spotted crossing the border at about 10:30 local time (01:30 GMT).
One of the South Korean warplanes involved in the operation, a KA-1 light attack aircraft, later crashed, but its two pilots escaped unhurt.
The plane fell to the ground in Hoengseong County, east of Seoul, soon after take-off from an air base in the nearby city of Wonju, according to the air force, quoted by Yonhap.
