HONG KONG, April 30 (Reuters) - Six spot bitcoin and ether exchange traded funds (ETFs) gained in their Hong Kong debut on Tuesday with the three bitcoin ETFs < 3008.HK> climbing more than 3% in early trade.

Cryptocurrency is banned in mainland China, but Hong Kong has been promoting itself as a global digital asset hub, part of a drive to maintain its allure as a financial center.

(Reporting by Summer Zhen and Sam Shen; Editing by Edwina Gibbs)