If both of these factories are managed by a single management, then you can cover the employees of the new factory under the Registration Certificate of EPF and ESI under the existing company. If the new factory is situated away from the present factory for which RCs are available, you can take subcodes for ESI and EPF. For EPF, you can even register the employees of the new factory without a subcode, but it is advisable to get a subcode for ESI.
If the new factory is separate from the existing establishment by all means, with a separate balance sheet, then it is a separate independent establishment. In such a scenario, taking ESI registration is not possible. For the registration of EPF, there is a scope of getting voluntary registration. But that process involves a lengthy process because voluntary registration is granted by the Central PF Commissioner and not by the regional offices of EPFO. For ESI, there is no voluntary coverage. However, you can get registration by including some casual workers for a single day and exiting them on the other day. This method has worked in many establishments that have sought guidance from me, and you can also follow this approach.