( CNN ) -- At least 20 people were killed and six injured Wednesday in a mine explosion in northeastern Colombia near the border with Venezuela , the government-run Colombian Institute of Geology and Mining , known by the acronym Ingeominas , reported . `` At this time , personnel from Ingeominas are at the scene of the accident dealing with the emergency with a group of institute rescue workers aided by the 5th Brigade of the national army , who brought in a helicopter for possible rescue efforts and to transport the victims , '' the institute said in a written statement . Earlier , a spokeswoman for the national civil defense agency said that more miners could still be in the mine , although an exact number was unknown . Hellen Garcia said that authorities believe as many as 30 could have been affected by the explosion . Garcia said five injured people were taken to two hospitals , but one of them died . Four bodies were taken out of the mine , she said . The remaining miners are 1,200 meters , or almost 4,000 feet , below ground , and the rescue operation by civil defense , Red Cross and government crews was expected to last through Thursday , Garcia said . Yamile Rangel Calderon , mayor of the municipality of Sardinata , said the mine is known as La Preciosa , or The Precious One . `` This is one of the oldest mines in the region and one that has some of the best safety and quality controls , '' she said . `` They have been exporting coal for many years . '' Calderon identified five of the miners who died as Manuel Aparicio , Gustavo Mendez , Gustavo Garcia , Jorge Luis Valdivieso and Nelson Velosa Fuentes . The blast happened around 7 a.m. in the district of San Roque , Alvaro Silva , a government official in Sardinata , told the government radio service . An accumulation of methane gas apparently caused the explosion , the governor of the Colombian state of North Santander told the radio service . A 2007 explosion in the same coal mine killed 31 people , Garcia said . CNN 's Rafael Romo and CNN en Español 's Claudia Dominguez contributed to this report .
Colombia : A Colombian mining agency says 20 miners are dead . NEW : The agency says 20 miners were killed . The blast happened near Colombia 's border with Venezuela . A build - up of methane gas may be to blame , governor says .