Frankly, it was a pain.
NPM doesn't give the option to import passwords from Opera. I said OK, Opera uses Chromium so importing from Chrome (x64) should work. So I followed the instructions. Unfortunately to no avail. It created *.json file but it was only a few bits and when I tried to import it into NPM it returned an error.
So I exported the logins from Opera to a *.csv. Than I had to edit the file as per this instructions (thanks God I found it) to get a CSV format that fits into NPM. Only then I was able to import the logins into NMP.
Hope it helps others.