A dense fog engulfed Shanghai on Tuesday morning, affecting road, water and air traffic while at the same time transforming the city into a heavenly world as depicted in traditional Chinese watercolor paintings.

The fog started to set in early in the morning. At 5:46 am, the Shanghai Meteorological Service upgraded the fog warning from yellow to orange, the second-highest in a three-level system when visibility in the city's six districts－Songjiang, Minhang, Jinshan, Fengxian, Pudong and Chongming－dropped below 200 meters. The warning was cleared by 11:35 am.

In its densest moment, the view from the Huangpu River resembled that of a Chinese water town found in typical traditional Chinese watercolor paintings with the city's modern skyline largely blurred by the misty veil. The only few remaining visible included the soaring tips of the city's three tallest buildings, Jinmao Tower, Shanghai Tower and Shanghai World Financial Center.

Due to the heavy fog, about 40 outbound flights were canceled at the city's Pudong and Hongqiao international airports. More than 50 flights scheduled to land at the two airports were diverted to neighboring cities, according to the Shanghai Airport Authority. Takeoffs and landings resumed in the afternoon as visibility increased.

City traffic remained in good order as the city's traffic authority put up speed limits in major expressways and deployed 40 percent more traffic police than usual, according to local news portal Eastday. Cross-river ferries were suspended while emergency lanes were opened on a bridge and a tunnel for bikes and mopeds to cross the Huangpu River.

The fog was caused by drizzle during Monday night that increased the humidity in the air, said the city weather bureau, adding that another fog is expected on Wednesday morning.

Despite the fog, the city's air on Tuesday morning was good, with PM2.5 staying below 50.