Best suggested way is to do V2V using VMware standalone convertor or any others.
So there wont be much down time comparitively to others.
You can use move-vm powercli cmdlet to move a VM between datacenters.
If both datacenters are managed by smae vCenter it's pretty straight forward.
Use the following link for reffrence;
if you have vCenter, you can power down the guest and cold migrate across datacenters. Assuming we are talking about virtual datacenters within vCenter. If not, then as already advised, use Converter.
Perfect - that's my question answered too, thanks :-)