Police have confirmed four Japanese construction workers have died after being recovered from inside a mountain tunnel where they were trapped following an explosion earlier this week. The blast occurred on Thursday inside a 2.8-kilometre highway tunnel being built in Minami Uonuma, about 180 kilometres northwest of Tokyo. It took more than two days for rescuers to be able to enter the tunnel because of dangerously high gas levels. A fire department spokesman says the workers were taken to hospital where they were confirmed dead.