Actress Lupita Nyong'o has written a moving tribute to her Black Panther co-star Chadwick Boseman, terming his death as "a punch to my gut".

Chadwick died on 29 August aged 43 after battling colon cancer for four years.

Lupita wrote on Instagram: "I write these words from a place of hopelessness, to honor a man who had great hope. I am struggling to think and speak about my friend, Chadwick Boseman, in the past tense. It doesn't make sense."

She recalled the experience of working with Chadwick in the Marvel superhero film.

"He showed up to every rehearsal and training and shoot day with his game face on. He absorbent. Agile. He set the bar high by working with a generosity of spirit, creating an ego-free environment by sheer example, and he always had a warm gaze and a strong embrace to share," she said.

"He seemed to really love himself; he expressed who he really was, even when it meant he didn't smile when you thought he should. He accepted himself. And perhaps that's why he was capable of loving so many so deeply."

Lupita posted a photo of her laughing with Chadwick