A large number of passengers are stranded at the Beijing Capital International Airport on Monday because of the weather. Provided To China Daily

Even though heavy rain didn't arrive at Beijing Capital International Airport as predicted by 5 pm, more than 600 flights were canceled or delayed because of intermittent thunderstorms on Monday.

Worse weather is predicted for the vast southern regions of China in coming days. Downpours are forecast to arrive on Tuesday and last until Thursday.

The national meteorological authority announced on Monday that rain would cover 1 million square kilometers, the widest area of storms this year.

Also on Monday, the national flood control authority released an emergency response plan to encourage increased readiness by local authorities.

As of 3:30 pm, the intermittent rain in Beijing affected 698 flights through cancellations or delays at the city's major airport, according to the Mirror newspaper.

The Beijing Meteorological Bureau said strong rainfall would start on Monday night, bringing with lightning, high winds and hail in certain regions.

The airport also warned that rain would continue to affect flights through Wednesday.

Storms in China's southern regions were expected to be harsh - "the strongest torrential rainfall with the largest coverage this year", Zhang Fanghua, chief forecaster at the Central Meteorological Observatory, said on Monday.

Daily rainfall is expected to exceed 50 millimeters in the south, with pockets of heavier precipitation exceeding 100 millimeters, Zhang said.

"Some cities in Hunan and Jiangxi provinces may see supertorrents, with rainfall exceeding historical records," she said. "Extreme daily rainfall in some regions could reach 350 millimeters."

Heavy weather is expected to peak on Wednesday and then trickle down through Thursday before weakening and moving northward, which will affect Henan and Shandong provinces, the observatory predicted.

"The heavy rains will increase the risks of flooding and geological disasters in the southern regions, which have been hammered since May," the chief forecaster said.

The storms are the result of summer monsoons and a strong cold front in the northeast, said Niu Ruoyun, another forecaster at the observatory.

In response to the increasing risk of floods and secondary disasters, the State Flood Control and Drought Relief Headquarters released a Level 4 emergency response plan, the lowest level in the four-tier national response system. It is the first such issuance this year.

Since the start of flood season on May 21, China has seen rainfall 18 percent higher than average, which has especially affected southern rivers. Rainfall at Taihu Lake has been 75 percent above normal, the authority said.

As of June 8, 15 provincial areas in South, Southwest and East China have been hit with floods and secondary disasters responsible for the deaths of 83 people. Direct economic losses reached 14.4 billion yuan ($2.2 billion), the headquarters said.