A massive king cobra was caught in a drain at a drug rehab centre in Thailand.

Terrified nurses called wildlife rescuers after hearing the serpent's loud hissing near the entrance ramp of the Ban Sala Dan Health Center in Krabi province on February 26.

Volunteers arrived at the scene and found the venomous 13ft reptile hiding under concrete drain covers.

Footage shows the team lifting the slabs of concrete and locating the cobra. They dragged the snake onto the tiled floor as it hissed violently in protest.

The snake was sealed inside a sack and later released into the wild.

A rescue officer said: 'The cobra may have been swept into the drain after recent heavy rains.'

Researchers found that 7,000 people are treated for snake bites each year in Thailand. Suchai Suteparuk from the Division of Toxicology at Chulalongkorn University reported that 30 of those die, with cobras being the biggest killer.