british citizen wanting to obtain chinese visa whilst visiting delhi

My 18 year old son is travelling in India at the moment and has a flight booked out of Sri Lanka to Malaysia on the 30th Oct then he will fly into Hong Kong on the 2nd of November but he needs to obtain a visa for China whilst he is in Delhi. He will land in Hong Kong on 2nd November and travel through China into Japan leaving Japan on the 5th of December to arrive home to Heathrow London, England on the 5th Dec. He has proof of his flights with him. Please could you tell me what other paperwork he needs to obtain a single entry to China. Many thanks Mrs Rogai.