A gas outburst incident in a tunnel in Dafang county, southwest China's Guizhou Province on Tuesday killed 12 people and injured another 12, Xinhua has reported.

The rescue operation ended on Wednesday morning after 14 hours. All 12 people previously reportedly to be trapped in the tunnel have died, and the injured are in stable condition after being hospitalized.

According to media reports, three of the dead were local residents in Guizhou Province and the others were migrant workers from Hubei and Yunnan provinces.

The incident occurred at around 2:50 p.m. on Tuesday in a 2,548-meter-long tunnel intended to hold a high-speed rail line. Around 2,000 people, including medical workers, fire fighters and rescue staff, were involved in the rescue operation.

An investigation into the cause of the incident is underway.