Visitors and staff at Thailand's Khao Kheow open zoo gathered today to celebrate its senior hippopotamus resident Mae Mali's 55th birthday, with a special cake made from colourful tropical fruit and vegetables.

Mae Mali, which name translates to Mother Jasmine in Thai, is the country's oldest-known hippopotamus, and came out to nibble on the fruit as spectators sang happy birthday to her.

Hippopotamuses have a life expectancy from 40 to 50 years typically.

"Mae Mali is now a grandma. We have been taking great care of her in regards to her health, food, and environment. Mae Mali cannot reproduce anymore because she's quite old. But we will still take great care of her so that she can become one of the longest living hippopotamuses in the world," said zoo's director.

According to Khao Kheow, the 55-year old hippopotamus gave birth to a number of offspring in her younger years and all 21 of her children and grandchildren can be found in other zoos across the country.