I wonder how come this simple question is causing such a confusion. "Good morning." in Japanese is おはようございます(ohayou-gozaimasu) for polite/formal situation or おはよう(ohayou) for casual situation. We don't have exact equivalent for "Good afternoon." You can use konnichiwa in the afternoon before sunset. 「お早うございます/お早う」is correct. We normally write them in hiragana, not kanji, but it's no problem.

@ Chihiro_ito Thank you, it is not the problem with the Japanese, It was the problem who claimed to be the Native Japanese.

お早う お早うございます Note: When I say it to the Japanese in Japan, they understand what I meant. But, when it was posted on Italki answer board and was selected as the best anwer. The native Japanese speaker name Chi sent me an email claiming it was wrong. I wonder, how are the Japanese say good morning in their own language

ohayou gozaimasu=>good morning. konnichiwa=>good day. konbanwa=>good night. "good afternoon" nihon go de ha nan desu ka ?

Hello 唐朝来客, "Good morning" in Japanese: Ohayo gozaimasu おはよう