Happen, take place: xảy ra, diễn ra, with the event after the verb

Xảy ra and diễn ra both mean "happen", but they share out the work. Xảy ra is for things nobody planned: accidents, fires, incidents, disputes. Diễn ra is for planned events: meetings, festivals, elections, matches. Vụ tai nạn xảy ra lúc 7 giờ sáng. The accident happened at 7 a.m. Lễ hội diễn ra trong ba ngày. The festival runs for three days.

The usual order is the event, the verb, then the time or place. But the event can also come after the verb, especially with xảy ra. A news report often starts with the place or time, then xảy ra, then what happened: Tại một kho hàng ở ngoại thành đã xảy ra hỏa hoạn. A fire broke out at a warehouse on the outskirts. A headline can even begin with the verb: Xảy ra cháy tại chung cư … Fire breaks out at … apartment block. This order presents the event as sudden news.

A few verbs of appearing work the same way: xuất hiện (appear) and biến mất (disappear). Trên mạng xuất hiện nhiều tài khoản giả. Many fake accounts have appeared online.

In conversation, xảy ra is common: Có chuyện gì xảy ra vậy? What happened? The simplest everyday question, though, is Có chuyện gì vậy? Diễn ra is mostly written; in speech people say có or tổ chức: Cuối tuần này có hội chợ. There's a fair this weekend.