German chancellor Angela Merkel let hundreds of thousands of migrants and refugees into Germany in 2015 because she feared closing the borders would look back on television.

Merkel was set to close the borders in September of 2015, when she was warned by aides that 40,000 migrants could move into Germany in one weekend, but she pulled back last minute, a book published this week claims.

After the warning, Merkel endorsed measures to close the border in a phone call with top officials, including the interior minister, Thomas de Maizière, and thousands of police officers were secretly deployed to the Austrian border.

German media had learned of the police deployment at the Austrian border, and agreed to a reporting blackout for security reasons, but Merkel changed her mind after de Maizière asked a leading German policeman: 'Can we live with the images that will come out of this?'

Angela Merkel was set to close the borders in September of 2015, when she was warned by aides that 40,000 migrants could move into Germany in one weekend, but she pulled back last minute

'What happens if 500 refugees with children in their arms run towards the border guards?' he added, according Robin Alexander, a leading German political journalist in the new book, Driven by Events: Merkel's Refugee Policy, the Sunday Times reported.

When leading German police man Dieter Romann told de Maizière that police would be making the decisions in real time on the ground, Merkel decided to keep the border open.

As a result, Germany's borders stayed open for another 180 days, during which thousands of migrants entered the country.

The border was finally closed in March 2016, when Balkan states cut off the migration route.

Alexander argues in the upcoming book that Merkel's welcome policy toward migrants was down to a lack of courage.

'In the end, Merkel refused to assume responsibility even as everything was in place to close the borders, so they remained open — without an explicit decision,' Alexander wrote.

After thousands of police officers were sent to the border, interior minister Thomas de Maizière asked if they could 'live with the images that will come out of this' and Merkel pulled out of the mission

Meanwhile, Merkel told a crowd in Germany last week that the number of migrants drowning as they try to cross the Aegean had gone down dramatically, but that there was still more to do to protect the EU's outer borders and curtail illegal trafficking.

Germany has taken in one million refugees and migrants since 2015, under a generous policy which Merkel has defended in the teeth of criticism including from new US President Donald Trump who called it a 'catastrophic mistake'.

In recent months, the anti-immigrant Alternative for Germany (AfD) party has been gaining in the polls and currently sits at 15 per cent ahead of the September elections.

Merkel suffered a setback Friday when the upper house of parliament rejected a proposal to declare three North African states 'safe countries of origin' in refugee law.

Meanwhile, Merkel said that there was still more to do to protect the EU's outer borders and curtail illegal trafficking. Pictured above, police escort refugees to a train bound for Dortmund at the main railway station in September 2015

The proposed designation for Algeria, Tunisia and Morocco aimed to make it easier for Germany to deny asylum requests from their citizens on the grounds that they were safe in their home countries.

The designation, which presumes a government does not systematically persecute opponents, would also aim to deter citizens of the three Maghreb countries countries from illegally heading to the EU in future.

Merkel suffered a setback Friday when the upper house of parliament rejected a proposal to declare three North African states 'safe countries of origin' in refugee law.

The proposed designation for Algeria, Tunisia and Morocco aimed to make it easier for Germany to deny asylum requests from their citizens on the grounds that they were safe in their home countries.

The designation, which presumes a government does not systematically persecute opponents, would also aim to deter citizens of the three Maghreb countries countries from illegally heading to the EU in future.