Ethiopian state radio said on Saturday those killed were part of a congregation attending a service to commemorate an Orthodox Christian saint. The broadcast made no mention of how many people had been wounded.
Rescuers combing through the cavernous structure said they might recover more bodies from the disaster, which occurred in a remote part of northern Ethiopia on Monday.
News has been slow to trickle out of the area, which lies about 300 km (190 miles) north of the capital, Addis Ababa.
Buried by rubble
"The rescue effort is still progressing, as it was feared many more may have been buried by rubble after the church caved in without warning," Tarekenge Emajnue, information officer for the Gonder region, told Reuters by telephone.
State radio quoted police as saying the toll at the Mewa Tsadkan Gabriel church had reached 15.
Tens of thousands of worshippers flock to the church from across northern Ethiopia to pray and give alms on the festival of Saint Gabriel, an important date in the calendar of Ethiopia's Orthodox Church.
It was unclear how many people were inside when the church's ceiling collapsed, but such rock churches often can accommodate scores of worshippers.
A second Jerusalem
The site was known to be among three of the first rock-hewn churches, built by the 13th-century Ethiopian King Lalibella, a ruler famed for his piety.
A town in northern Ethiopia named after the king boasts more of the spectacular churches with exquisite carvings, which some say were constructed to create a second Jerusalem in the heart of Ethiopia.
The churches are an important tourist attraction for the country of 67 million, drawing visitors from around the world, lured by the cultural artefacts of a Christian civilisation dating back to the fourth century.