A coal mine explosion has killed at least 20 workers and wounded six others in the northeastern Colombian department of Norte de Santander, emergency agencies and the mine company said Wednesday.

"At the moment we have information of 20 workers dead and six wounded. Currently, we are in the rescue process ... we are waiting to decrease the gas concentrations," said Gabriel Tamayo, the mine's legal representative.

The explosion occurred around 6:50 a.m. local time (11:50 GMT) inside the coal tunnel known as La Preciosa, located in the town of Sardinata, Norte de Santander.

Tamayo said that they have only found five bodies. "When there are high concentration of gases, the people die in seconds ... we have found very high concentration of gases that indicate that there is no one alive inside."

As for the cause of the explosion, the manager said he "cannot tell for sure what happened, because no one has entered into the mine."

The mayor of Sardinal, Yamile Rangel, told local media that at least 30 workers were in La Preciosa at the moment of the incident.

In a statement, the Colombian Institute of Geology and Mining, or Ingeominas), said that a rescue team went to the scene to support rescue efforts that have been interrupted many times during the day, because of the monoxide concentration.

"Ingeominas staff is at the place where this accident took place ... in association with the Colombian Army that has provided a helicopter to help the rescue work," said the statement posted on the Internet.

In mid-2010, 73 miners died in a mine blast in Amaga, a town of the Antioquia department in northwestern Colombia. It was considered as the worst mining tragedy in the recent history of Colombia.