Colombia coal mine blast kills 6

Six workers died and three others were missing after an explosion at an underground coal mine in northern Colombia, authorities said on Wednesday.

The incident at Corrales in Boyacá department, 220km north of capital Bogotá, occurred early on Tuesday and was likely caused by an accumulation of methane gas, according to officials.

The blast also left a 100-150m crater, hampering rescue efforts.

"We regret the death of the miners in Corrales, @GobBoyaca. My condolences to their families. A strong call to companies to comply with the safety standards that guarantee the lives of our miners. @ANMColombia," Colombian mining minister Germán Arce said on Twitter.

The name of the mine's owner was still not known at the time of publication and authorities did not say if the operation was legal.

An investigation will be launched immediately to determine the cause of the incident, officials said.

Mining accidents are common in Colombia, where illegal exploration remains rife despite government efforts to improve the sector's regulatory framework.

Some 114 people were killed at local mines last year, according to official figures. The worst mining tragedy in Colombia's recent history occurred in 2010 when 73 workers died in a blast in Amaga, in the northwestern department of Antioquia.