The UK's largest car manufacturing plant is "unsustainable" if the UK leaves the European Union without a trade deal, owner Nissan says.
The Japanese company's global chief operating head told the BBC people had to understand the EU was the Sunderland factory's biggest customer.
Ashwani Gupta said that Nissan's commitment could not be maintained if there was not tariff-free EU access.
Nissan has invested billions of pounds in the plant, which has 7,000 workers.
His comments come despite the Sunderland site surviving this week's announcement on the Japanese giant's global restructuring programme.
Mr Gupta said: "You know we are the number one carmaker in the UK and we want to continue. We are committed. Having said that, if we are not getting the current tariffs, it's not our intention but the business will not be sustainable. That's what everybody has to understand."
Crucial talks
He also said that any plans for its strategic partner and 43%-shareholder Renault to take up spare capacity at Sunderland would be a matter for the French carmaker. The French government has a 15% stake in Renault.
This is not the first time that Nissan has pleaded with UK and EU negotiators to ensure that the 70% of cars manufactured at Sunderland which are sold in the EU can avoid tariffs of 10% under World Trade Organisation rules - the legal default position if a deal is not struck.
Those talks resumed this week, with the differences between the UK and EU being described on all sides as deep and wide.
Last week, the EU's chief negotiator Michel Barnier said the EU would consider a two-year Brexit delay, which was rebuffed by his UK counterpart David Frost, who told MPs the government's policy remains not to extend the transition period beyond the end of the year.
Under an agreement signed last year, the UK has until the end of this month to decide whether it wants to request such an extension so the coming weeks are crucial.
The comments by Nissan may dampen hopes raised just last week when the company said that while it was closing plants in Spain and Indonesia, it remained committed to Sunderland.
An announcement by Nissan that Renault might take the European lead in the companies' global manufacturing alliance (which also includes Mitsubishi) by taking up an estimated 20% spare capacity at Sunderland were quashed for the foreseeable future by Renault last week, when it said it had no current plans to move in to the UK.
