i am travelling from new delhi to auckland have a 20 hr stop at guangzhaou . how do i get a visa

You need to apply visa at the local Chinese Embassy. People who hold passports of countries on the following list https://www.travelchinaguide.com/embassy/pdf/hongkong-visa-free.pdf do not need visas to Hongkong. If your nationality is not on it, you may use the China visa.