发生 (fāshēng, happen) means happen in Chinese. You can use it to ask What happened? or to say An accident happened.
发生了什么事？
Fāshēng le shénme shì?
What happened?
昨天这里发生了意外。
Zuótiān zhèlǐ fāshēng le yìwài.
An accident happened here yesterday.
To say that someone had an accident, add the person before 发生.
他发生了严重的意外。
Tā fāshēng le yánzhòng de yìwài.
He had a serious accident.
Literal: He happened a serious accident.