European Catholic leaders have expressed concern that the decision by British voters to leave the European Union threatens unity across the continent, but they also said the EU bloc must rethink its values and priorities.

The concerns arose after voters decided to exit the EU by 52 per cent to 48 per cent. The decision led Prime Minister David Cameron to announce his resignation and sent shock waves through world financial markets.

In London, Cardinal Vincent Nichols, president of the Bishops' Conference of England and Wales, said the vote must be respected and that the United Kingdom is setting out on a "new course that will be demanding on all".