Japanese Prime Minister Kishida Fumio has sent a letter of condolence following the death of Vietnam's top leader, Nguyen Phu Trong.

The Vietnamese Communist Party's General Secretary died on Friday at the age of 80.

In the letter sent on the same day to Vietnamese Prime Minister Pham Minh Chinh, Kishida said he was "surprised and saddened" by the news.

Kishida expressed "his deepest condolences" to the government and people of Vietnam and to the bereaved family on behalf of the government and people of Japan.

He also expressed his sincere respect for the late leader's "significant contributions to Japan-Vietnam relations."

He said Trong "had demonstrated great leadership in building close cooperation between Japan and Vietnam as comprehensive strategic partners in a wide range of fields."