In one of the mosques in New Zealand during jummah after the first athan most of the brothers including imam used to offer Zuhr (4 rakath) salah individually and after 2nd athan jummah speach and offer 2 rakath jumma salah in jamath. But I do not offer zuhr salah on Fridays as it replaces jummah. But I couldn’t ask the imam as don’t aware of saheeh hatheeths on these. Please clarify on this with hatheeth to ask the imam.
Answer:
In the name of Allah, the most Beneficent, the most Merciful.
The Jummah Salah is a substitute for the Zuhr Salah on Friday. There is no need to pray Zuhr on Friday. (Fatawa Darul Uloom Deoband p.137 v.5)
It is possible that the Imam and the followers may be praying four rakaats sunnah before the Jummah afer the first Azan.
Saaiduna Ibn Abbas 
reports that the Prophet of Allah 
used to perform four rakaats of Salah before and after the Jummah Salah” (Tabraani)
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham