Angela Merkel's expected to be re-elected as Germany's Chancellor in elections being held today.

Tens of millions of people are going to the polls in elections, with Merkel's party the Christian Democrats holding a massive lead in the polls.

But the chancellor may be forced into a coalition with her biggest rivals if her current partners can't keep their seats in the parliament.

There are only two situations in which Angela Merkel might lose her position as chancellor.

The first is if her current coalition partners, the Free Democrats, don't make it back into the Bundestag.

Under Germany's electoral laws, a party needs to get 5 per cent of the vote in order to qualify for seats in the parliament.

The Free Democrats are polling at around 5.4 per cent - and if they go much lower, Merkel won't be able to rely on them.

If this is the case then the most likely option is a grand coalition between Merkel's Christian Democrats and the biggest opposition party, the Social Democrats - renewing the partnership from Merkel's first term.

But that partnership could be unpopular with voters - and the Social Democrats could opt out, allowing them to set up a government of their own with the Greens and some left-wing parties.