If approved, the measures will end Switzerland's free movement of people agreement with the European Union.

Fiercely independent Switzerland is not a member of the EU, but has adopted large sections of EU policy.

Brussels has already warned the Swiss that they cannot just choose the aspects they like.

The vote comes amid increasing debate across Europe about migration and the impact of free movement of people.

Those in favour of mass migration says the policy will benefit the Swiss economy

But many other people believe mass immigration is harming Switzerland

The referendum will be keenly watched by other European nations debating their immigration policy

Analysts had expected a tight race, but the BBC's Imogen Foulkes in Switzerland says it appears to be incredibly close.

The referendum needs more than 50% of the vote to pass.

Switzerland's economy is booming at the moment, and unemployment is low, but many Swiss worry about immigration.

A quarter of the eight million-strong population is foreign, and last year 80,000 new immigrants arrived.

Since 2007, most of the EU's 500 million residents have been on an equal footing with locals in the Swiss job market - the result of a policy voted into law in a 2000 referendum.

But a coalition led by the right-wing Swiss People's Party now wants to reverse this deal, saying it was a huge mistake.

Supporters of quotas believe free movement has put pressure on housing, health, education, and transport - and they also argue that foreign workers drive salaries down.

But the Swiss government and business leaders say free movement is key to Switzerland's economic success, allowing employers to choose skilled staff from across Europe.

Our correspondent says that abandoning free movement could limit Switzerland's access to Europe's single market, where over half its exports are sold.