ICAO recommends the use of standard "PANPAN" and "MAYDAY" calls instead of "declaring an emergency" as failing to use non-standard phraseology has previously resulted in confusion and aircraft handling errors:
https://www.hkatc.gov.hk/HK_AIP/aic/AIC21-12.pdf
https://www.skybrary.aero/bookshelf/books/115.pdf