Residents of western Beijing's Shijingshan district wade through several centimeters of water in a flooded street on Wednesday. The village, like several other parts of the capital, has seen flooding from heavy rain due to outdated drainage facilities.Photo: Li Hao/GT

An orange alert, the second-highest in China's four-tier warning system, was issued in Beijing on Wednesday as torrential rain deluged the capital, disrupting traffic and forcing the cancellation of flights.

Around 70 millimeters of rain fell in central and southern Beijing over just six hours, according to the city's meteorological authority. Heavy rain is expected to last until Wednesday night and may exceed 100 millimeters.

The capital issued a blue storm alert on Tuesday morning, raised it to a yellow alert on Wednesday morning and ultimately raised it yet again in the early afternoon.

The Beijing Water Authority also issued the first-ever flood warning at noon on Wednesday for the North Canal, including two orange alerts for two sections of the canal, the heaviest flooding it has seen in 20 years, The Beijing News reported.

Fish were even spotted around a storm drain at Beijing West Railway Station at noon as the drain overflowed, according to the China News Service.

The 600-year-old Forbidden City, however, remained free of flooding, largely due to its sound drainage system, The Beijing News reported.

The rainstorm also impaired the city's transportation system. A total of 226 flights at Beijing International Airport had been canceled as of 4 pm due to the rain. Train services were also disrupted, the Xinhua News Agency reported.

Several subway lines were delayed Wednesday morning, and some subway stations were temporarily closed, the Beijing Subway said on its official Sina Weibo account.

The torrential rain is reminiscent of the extreme rainfall that lashed Beijing on July 21, 2012 - the heaviest in 61 years - leaving 79 citizens dead. However, Beijing meteorological authorities confirmed Wednesday that the present spate of rain is less severe than that of 2012, The Beijing News reported.

Although the rain fell continuously for 30 hours, 13 hours more than four years ago, the intensity of the precipitation is lower. Only 56.8 millimeters fell per hour this July, while over 100 millimeters of rain fell each hour on average in the 2012 storm.

In terms of the severity of convection currents - such as the frequency of thunderstorms and hail - the downpour drenching Beijing is also less harsh than the relentless rain that wreaked havoc in several southern Chinese provinces in May and June, Ma Xuekuan, a weather forecaster at the China National Meteorological Center, was quoted as saying by the Beijing Morning News on Wednesday.

The national meteorological authority also maintained its orange alert for rainstorms across the country on Wednesday. Torrential rain will hit parts of North China's Tianjin and Hebei Province, Northeast China's Liaoning and Jilin provinces, East China's Shandong and Jiangsu provinces, Central China's Hubei and Hunan provinces and Southwest China's Yunnan Province from Wednesday to Thursday, with rainfall of up to 240 millimeters in some places.

Tourists visit the Forbidden City in rain in Beijing, capital of China, July 20, 2016. Beijing's meteorological bureau issued an orange alert for rainstorm Wednesday noon.Photo: Xinhua

Tourists visit the Forbidden City in rain in Beijing, capital of China, July 20, 2016. Beijing's meteorological bureau issued an orange alert for rainstorm Wednesday noon.Photo: Xinhua

Buildings are shrouded in rain as seen from a car window in Beijing, capital of China, July 20, 2016. Beijing's meteorological bureau issued an orange alert for rainstorm Wednesday noon. Photo: Xinhua