Black swans are seen at the Nanning Garden Expo Park in Nanning, south China's Guangxi Zhuang Autonomous Region, April 9, 2020. (Photos: Xinhua)

Aerial photo taken on April 9, 2020 shows a view of the Nanning Garden Expo Park in Nanning, south China's Guangxi Zhuang Autonomous Region.

Aerial photo taken on April 9, 2020 shows a view of the Nanning Garden Expo Park in Nanning, south China's Guangxi Zhuang Autonomous Region.

Photo taken on April 9, 2020 shows flowers in the Nanning Garden Expo Park in Nanning, south China's Guangxi Zhuang Autonomous Region .

Black swans are seen at the Nanning Garden Expo Park in Nanning, south China's Guangxi Zhuang Autonomous Region, April 9, 2020.