Most British cities sell more of their exported goods to Europe than anywhere else in the world, research shows.
Centre for Cities said a study of 62 cities found that only Hull sold more goods and services to a different destination.
The think tank said its findings underlined the importance of securing the best trade deal in the negotiations over Brexit.
The report said British cities would have to "dramatically" increase trade with other countries to compensate for a downturn in exports to the EU.
Britain's top exporting city is Sunderland, followed by Worthing and Slough, said the think tank.
Alexandra Jones, chief executive of Centre for Cities, said: "Securing the best possible EU trade deal will be critical for the prosperity of cities across Britain, and should be the Government's top priority as we prepare to leave the single market and potentially the customs union.
"While it's right to be ambitious about increasing exports to countries such as the US and China, the outcome of EU trade negotiations will have a much bigger impact on places and people up and down the country.
"It's also important that the Government aims to reach trade agreements covering as many sectors as possible, rather than prioritising deals for high-profile industries based in a small number of places.
"Broad trade agreements for all goods and services will help every city to build on its exporting strengths.
"The UK faces a major challenge in boosting productivity and wages, and increasing the value and volume of city exports will be crucial in addressing those issues.
"National and local leaders need to consider how they can make cities more attractive to exporting firms.
"Improving skills and infrastructure across the UK will be vital in this, and should be a central part of the Government's industrial strategy."
A Government spokesman said: "As the Prime Minister has said, we will pursue a bold and ambitious free trade agreement with the EU that allows for the freest possible trade.
"But we will also take advantage of the opportunities leaving the EU presents, forging stronger trading links with markets across the world.
"We are supporting UK businesses in every region of the UK as we do this, through the Government's Industrial Strategy and our new export hub with free advice, financial support and live export opportunities."