A Chinese helicopter allegedly harassed Filipino researchers conducting a marine survey off an island in the South China Sea.

Footage shows the Communist state aircraft hovering over the scientists doing marine research on two barren sandbars called Sandy Cay on March 23.

The helicopter and China Coast Guard (CCG) ships reportedly tried to block the Philippine government vessels from entering the contested area.

CCG spokesman Gan Yu said in a statement that the Chinese personnel dealt with 'illegal activities' by Philippine staff who 'ignored China's warnings and dissuasion'.

Meanwhile, Philippine Coast Guard spokesperson Commodore Jay Tarriela said the research mission was a success despite the 'dangerous manoeuvres' of the CCG.

He said: 'Amid their (Chinese) dangerous maneuvers, blocking operations, and the Chinese maritime militia's illegal presence there, we were able to complete our marine scientific research.'

China currently lays claim over almost the entire South China Sea, one of the world's busiest sea lanes. But a United Nations-backed tribunal in 2016 deemed its claims groundless.

There have been dozens of run-ins between China and Philippines in recent months as the territorial dispute intensifies.