Workers celebrate as they dug through the tunnel under Chongqing Jiangbei International Airport in southwest China's Chongqing Municipality, Nov. 7, 2020. Chinese workers on Saturday dug through the first railway tunnel under airport in Chongqing. The 4.49-km tunnel under Chongqing Jiangbei International Airport is expected to be put into service in 2021. (Xinhua/Tang Yi)

Workers are busy at the construction site of the tunnel under Chongqing Jiangbei International Airport in southwest China's Chongqing Municipality, Nov. 7, 2020. Chinese workers on Saturday dug through the first railway tunnel under airport in Chongqing. The 4.49-km tunnel under Chongqing Jiangbei International Airport is expected to be put into service in 2021. (Xinhua/Tang Yi)

An airplane flies over the tunnel under construction under Chongqing Jiangbei International Airport in southwest China's Chongqing Municipality, Nov. 7, 2020. Chinese workers on Saturday dug through the first railway tunnel under airport in Chongqing. The 4.49-km tunnel under Chongqing Jiangbei International Airport is expected to be put into service in 2021. (Xinhua/Tang Yi)

A worker checks the safety of the tunnel under construction under Chongqing Jiangbei International Airport in southwest China's Chongqing Municipality, Nov. 7, 2020. Chinese workers on Saturday dug through the first railway tunnel under airport in Chongqing. The 4.49-km tunnel under Chongqing Jiangbei International Airport is expected to be put into service in 2021. (Xinhua/Tang Yi)