CHENGDU, Feb. 25 -- The death toll has risen to three following a gas explosion in an incomplete road tunnel in Chengdu, capital of southwest China's Sichuan Province, on Tuesday afternoon.

According to the project undertaker, the Power China Road Bridge Group Co. Ltd., a body retrieved by rescuers at around 1 p.m. on Wednesday was one of the four construction workers it lost contact with when the blast happened in the No. 1 Tunnel of Wuluo Road at around 1:20 p.m. on Tuesday.

It is not known how many people were inside at the time of the accident.

One of the other two bodies recovered earlier has been identified as a local farmer. The other body has been burnt and can not be identified immediately.

The high concentration of gas in the tunnel is making the rescue very difficult, said Huang Xinchu, head of the rescue headquarters.

Local hospitals have taken in 20 people injured in the blast. Two of them are still in critical condition.

Wang Zhichang, an expert with the Chengdu Safety Inspection Bureau, who is with the rescue team at the blast site, said the tunnel has two lanes designed for traffic to flow in opposite directions. Workers had dug in 800 meters before the blast happened.

Ventilation has resumed in one of the lanes so that 110 rescuers aided with sniffer dogs can enter. Workers have blocked the other lane and are pumping in carbon dioxide to quench the fire and gas there, said Wang.

An investigation is under way into the cause of the incident.