"Since the sad news it feels uneasy when I look at my uniform as it now reminds me of him. He was very close to me. More of a brother than a friend.''
Mr Mestry saw his friend for the last time when he visited Queenstown with his wife last month.
Another friend and former colleague of Mr Singh's, Kritika Singh, said the news of his death was "heartbreaking''.
"I wish this just was a bad dream and when I wake up it will be just a dream.
"I will remember his life and him as a person in a positive, happy way with a big smile, just like the one he used to have.''
Ms Singh added he was a joy to work with and it was an "honour to be his friend''.
Mr Singh's friend from Auckland, Memory Kamalpreet Keani Teremate, said he was a "bright kid with so much potential''.
"Hearing about his loss was so shocking. I was so shattered, especially for his family back home.''
Mr Singh was the sole occupant of the vehicle in Sunday's crash. His body was reportedly taken to Invercargill and police are yet to release a formal identification.
The bus driver and passengers were not injured.
The collision happened less than 48 hours after a head-on crash on the same stretch of road, which left one man seriously injured and two people with minor injuries.