This autumn has been longer and warmer than previous years, prompting doctors to warn that it could lead to a rapid spread of flu infections.

"The flu virus is very active in a warm autumn and can reproduce and spread very quickly, especially for children and old people whose immune systems are weaker," said Cai Baiqiang, director of respiratory department in Peking Union Medical College Hospital.

"Because the autumn is longer than before, the flowering season in Beijing is also longer than usual, which can cause more asthmatic problems due to pollen."

The Beijing meteorological bureau said the average temperature this autumn has been more than 15 C. In previous years, the average temperature was less than 14 C.

"The major reason that is causing the warmer autumn is that the cold air from North China is weaker than during corresponding periods in previous years," said Zhang Qing, senior engineer from the Beijing climate center.

According to Zhang, this autumn started on Sept 6 and it has so far lasted for 50 days.

Meteorologists define autumn as the season when the daily temperature is between 10 C and 22 C. This autumn is expected to be as long as 55 days, compared to the average of 40 days.

"The change in Beijing is a reflection of the global issue - climate change," Zhang said.

In previous years, autumn has been gradually increasing. There were 30 days in 2000, 50 days in 2005 and 53 days last year.

In order to avoid infection, Cai said it is better for citizens to avoid crowded areas, to wear face masks when they need to go out, and to stay at home if they show fever-like symptoms.

However, the longer autumn does have the benefit of prolonged sightseeing of red leaves in Fragrant Hills Park.

The red leaves in Fragrant Hills Park are expected to last an additional two weeks this year.

"Only 50 percent of the leaves have turned red until now, but we usually see 3 quarters of them turn in other years at the same time," said Yao Jiang from Fragrant Hills Park.