Action must be taken to prevent other countries from fleeing the EU, German Chancellor Angela Merkel has said.
Speaking at a Christian Democratic Union party executive board meeting, Ms Merkel said the financial markets are very concerned that the EU is no longer governable.
She added that all 27 remaining EU countries must consult together on the way forward following Britain's vote to leave the bloc.
However, Ms Merkel maintained that it is not the right time to pursue a quick deepening of cooperation between eurozone member states.
Instead, the EU should act on popular concerns such as securing the bloc's borders, creating jobs and improving internal security, she said.
Foreign Secretary Philip Hammond said there will have to be a "trade-off" on UK access to the EU single market and migration controls.
France's foreign minister called for the UK to trigger the exit clause after a meeting with counterparts of the six EU founding states.
European leaders have reacted to the UK's historic vote to leave the EU.