BEIJING, July 20, 2016 (Xinhua) -- Photo taken by a cellphone shows vehicles stranded in water at a flooded tunnel outside the Beijing West Railway Station in Beijing, capital of China, July 20, 2016. Beijing's meteorological bureau issued an orange alert for rainstorm Wednesday noon. (Xinhua/Liu Guannan)

July 20 (Xinhua) -- An orange alert, the second highest of China's four-tier warning system, was issued on Wednesday as heavy rain hit Beijing, disrupting the traffic and forcing flights to be canceled.

Around 70 mm of rain fell in central and southern Beijing in six hours, according to the city's meteorological authority.

Heavy rain is expected to last until Wednesday night and may exceed 100 mm.

The capital issued a blue storm alert at 7:30 a.m. Tuesday and raised it to yellow on Wednesday morning before raising it again in the early afternoon.

A total of 169 flights have been canceled at Beijing International Airport due to the rain. Train services have also been disrupted.

The national meteorological authority on Wednesday also maintained its orange alert for rainstorms across the country.

Besides Beijing, torrential rain will hit parts of Tianjin, Hebei, Liaoning, Jilin, Inner Mongolia, Shandong, Henan, Jiangsu, Anhui, Hubei, Hunan and Yunnan from Wednesday afternoon to Thursday afternoon, with rainfall of up to 240 millimeters in some places.

The National Meteorological Center advised people living in the affected areas to prepare for possible floods, landslides and mud and rock flows, and those that live in mountainous areas should move to safe places.

China has a four-tier color-coded system for severe weather, with red being the most serious, followed by orange, yellow and blue.