HK work visa requirements

I’m afraid you cannot apply for the work entry permit after you enjoy free entry to enter HK. You should apply for it ahead of time in your home country.
In order to apply for the work entry permit, you need to provide copy of your passport, the completed application form attached with a passport-style photo, and proof of your academic qualifications and relevant work experience.
Your employer needs to provide the application form, the employment contract, copy of business registration certificate, copy of financial standing of the company, documents with details of company background, and detailed business plan.