In a statement after the talks Tony Woodley, general secretary of the T&GWU, said: "Clearly we are looking for as many jobs to return to Longbridge along with car making, but there is much to discuss."
The Chinese firm has secured only a short term licence on the site.
The licence is understood to last between six months and a year and allows Nanjing to 'lift and shift' equipment from Longbridge.
After the licence expires Nanjing would be required to come back to Longbridge landowners St Modwen with a decision on whether it intends to use the site to produce cars in Birmingham or transfer operations to China.
The Longbridge site is leased by St Modwen to MG Property Holdings and the administrators PricewaterhouseCoopers. However, the property company issued the licence to Nanjing.
St Modwen chairman Anthony Glossop said short term arrangements such as the Longbridge agreement were common.
He also said Nanjing could decide "to take everything to China and do nothing with the site".