A salt lake in northern China's Shanxi province has become a new tourist attraction after a portion of it recently turned red, state media reported.

Aerial footage of the lake released by China's state television CCTV showed red water on one side of the lake and green on the other, with a road cutting through the middle.

CCTV reported that the colour change was caused by a large amount of naturally-occurring algae, and said that the hotter the weather, the longer the red colour will last.

The red colour occurs when the amount of the micro-algae called dunaliella salina reaches a specific number, CCTV said.

The algae survives in saline environments and is normally green, but turns red due to heat and light because it holds the red-orange pigment beta-carotene, which scientists say protects it from UV radiation.

Local officials were cited as saying the phenomenon is an annual occurrence but it was not immediately clear why only one side of the lake had changed.

The lake, formed around 500 million years ago, is called "China's Dead Sea",