When was Hong Kong leased to Britain for 99 years by China

In formal terms the answer lies in the second Convention of Peking, signed on 9 June 1898. The ailing Qing Dynasty leased the New Territories to Britain for 99 years, starting 1 July 1898. The new additions were to make up 90 per cent of Hong Kong's land mass. The term of 99 years was fixed almost casually.