A drunken New Zealand man who thought it would be a good prank to pull a dog's tongue has suffered serious facial injuries after the dog bit his mouth.

The 39-year-old National Park resident was partying at a friend's house on Wednesday when he grabbed the large crossbreed dog and held it down while trying to grab its tongue.

The dog managed to free itself and lunged at the man's face, biting the corners of his mouth, Constable Conrad Smith said.

The man was taken to Taumarunui Hospital and later flown to Waikato Hospital. He was in a stable condition last night, a hospital spokeswoman said.

"He had lost a lot of blood," Mr Smith said. "It is likely he will need cosmetic surgery to repair the wounds."