Every spring, Beijing is invaded by so-called "April Snow" - poplar and willow catkins that float around and cover everything in sight.

But now it seems they are also a safety risk, with half of Beijing's fires in April blamed on the white fluff, according to the municipal fire department.

The department reported 686 fire alarms last month and 346 of them were reportedly spread by the highly-flammable catkins.

One of the most severe fires destroyed 90 electric vehicles in a parking lot in Beijing's Chaoyang District, requiring more than 50 fire engines to be sent to the scene.

The official cause of the accident has yet to be given, but the electric vehicle companies said they suspected that fireworks set off at a nearby wedding ignited the catkins, causing the blaze.‍

Beijing’s municipal government on Tuesday mobilized resources and personnel to help clear catkins from residential areas, schools, gas stations, warehouses, bus stops, historical buildings, parks and construction sites.

Over 400 fire engines and 300 water trucks also sprayed 8,750 tons of water over two days in these areas to stop catkins floating in the air.

Under urban landscaping campaigns in the 1980s, more than three million poplar and willow trees were planted along Beijing's roads and rivers.

According to the municipal landscaping bureau, poplars and willows can help combat air pollution: a single poplar tree with a 20-centimeter diameter trunk can assimilate 172 kilograms of carbon dioxide per year and stop 16 kg of dust, while discharging 125 kg of oxygen.

However, most of the trees planted in Beijing were female trees which produce massive amounts of catkins.

In addition to causing fire hazards, they are also a nuisance for urban residents who are allergic.

Du Jianjun from the landscaping bureau said that in recent years, the bureau has injected a substance into the trees to change their gender and reduce the amount of catkins produced.

"We can't solve the catkin problem simply by cutting down the trees. The current sex change program takes not only time, but also substantial costs and human resources," he said.

This year, the bureau will treat 400,000 of the two million poplar and willow trees in Beijing, Du said.

The bureau plans to solve the catkin problem by 2020.