Dear Supriya,
Employee numbers are given based on DOJ; actually, it's a primary key (unique number) if you have a HRIS (each employee has a unique EMPID), it is automatically generated. In your case, you can keep a record book where numbers can be entered incrementally so that it won't create any problems. Also, keep in mind that no employee should be given a retired EMPID because it may create problems when some employees are involved in a case or if the company has any labor issues.
If you know MS Access, MS SQL Server, or Oracle, design a database either opting for the auto option so that the next record number (EMPID) will be created automatically. Choose either Numeric or Varchar as the property of the field. If you choose a numeric value, EMPID can only be numeric data like 1241 or 4120. If you choose varchar as the data field, then you could use names like 142BGLR, 142CHN, etc.
Think about your company's future growth and choose a 4-digit or 5-digit format.
Thank you.