Do UK/NZ citizens need a visa before entering Hainan, or can we get one on arrival?

My friend, a British national, and I, a New Zealand citizen would like to visit Sanya, Hainan for a short holiday. We will be entering from Hong Kong. We currently reside in South Korea. Do we need to apply for a visa before we enter Hainan, or can we get the visa on arrival?
Many thanks,