(CNN) -- At least nine miners remain trapped in a South African gold mine after an underground fire, the Harmony Gold mining company said Wednesday.
South African emergency workers rescued eight other miners and brought them to the surface at the Doornkop mine, west of Johannesburg.
"Rescue teams continue the search for the remaining nine miners who are still unaccounted for," the company said in a prepared statement.
"The underground fire has been subdued, although conditions underground remain challenging."
It said the eight miners who were rescued were unharmed but would be kept under medical observation during the night as a precaution.
The fire is reported to have broken out about 1,733 meters (5,700 feet) underground around 6 p.m. local time Tuesday.
Harmony Gold spokesman James Duncan said seismic activity -- a magnitude-2.4 tremor that caused rock to fall -- may have caused the fire.
"The rock fell, damaged a cable, which we think caused a spark which then ignited something and caused the fire," he said.
"Obviously, this is all subject to inquiry. Our priority is finding the missing men."
All operations other than essential services at the mine have been suspended.
CNN's Marie-Louise Gumuchian and Nana Karikari-apau contributed to this report.