MUNICH (REUTERS) - She launched her re-election campaign just days ago, but German Chancellor Angela Merkel's immigration policies are already a target.

Speaking at a rally just outside Frankfurt on Monday (Aug 14), Merkel was booed and whistled by anti-immigration protesters throughout her 33-minute speech.

The group of around 100 "Alternative for Germany" supporters was heckling her from the crowd.

The party is expected to enter the national Parliament for the first time in next month's election - polling 7 to 9 per cent.

Merkel acknowledged her detractors' efforts, and said: "We can do this in a democracy where people are allowed to express their dissatisfaction, and to listen a bit is also not a bad thing."

Merkel drew boos mixed with applause when she thanked volunteers and professionals who helped the 890,000 migrants and refugees who arrived in Germany in 2015 following her decision to open the country's borders.

She added during her speech that Germany needed to do more to tackle the root causes of migration such as encouraging development in Africa.

Merkel is campaigning on a platform of economic stability and will be boosted by news that Germany's gross domestic product rose by 0.6 per cent in the second quarter.

Strong household spending, rising state expenditure and higher company investments consolidate the country's role as the euro zone growth engine.

Polls show Merkel's conservatives are set to emerge from the Sept 24 election as the largest party by a long shot, but are still in need of a coalition partner.