Does nginx write its error logs?

We look at nginx error logs for changes, but with some difficulties we take into account such extreme cases as file truncations, etc.

It would be useful to know if nginx writes its error log files on the fly or buffers entries in error logs. Buffering won't make much sense for error logs, but high performance in nginx can still be achieved.

We know that nginx buffers access log entries, but currently cannot find evidence that it does the same for error logs.