Nomvethe, who has scored twice in 2018/19, was initially due to retire this month, but will now see out the rest of the season with Usuthu.
AmaZulu confirmed the news on Twitter, saying: "AmaZulu FC can confirm that both the club and Siyabonga Nomvethe have agreed on a contract extension until end of the season. Bhele was due to retire at the end of 2018 but has agreed to stay on."
Bhele - the PSL's all-time top scorer with 123 goals - has enjoyed an illustrious 21-year career, turning out for the likes of Soweto giants Chiefs and Orlando Pirates, Italian trio Udinese, Salernitana and Empoli, Sweden's Djurgardens and Danish side Aalborg.
He also earned 82 caps for Bafana, scoring 16 times for his country among other accomplishments.