CHONGQING -- Four people were killed and nine others were injured in a blast that ripped through a highway tunnel under construction in Southwest China's Chongqing municipality on Monday afternoon, local authorities said on Tuesday.

According to the commission of transport in Wanzhou district of Chongqing, the blast occurred at about 3:10 pm Monday at the construction site of a section of the national highway linking Hubei and Sichuan provinces. One person was initially reported missing and 12 others were wounded.

As of midnight on Tuesday, rescuers managed to find the body of the missing individual, while three of the injured succumbed to their wounds despite receiving medical treatment.

The explosion was suspected to have been triggered by flammable gas. The site has been cordoned off and an investigation is underway.