German Chancellor Angela Merkel had said lessons should be learnt but cautioned against overly high expectations.

The German government on Monday pledged to improve the country's under-fire warning systems as emergency services continued to search for victims of the worst flooding in living memory, with at least 165 people confirmed dead.

The west of the country was deluged over two days last week, with torrents of water sweeping away trees, cars and bridges and destroying swathes of housing.

Many victims in Germany were found dead in sodden cellars after attempting to retrieve valuables, while others were swept away by the sheer force of the water.

A total of 117 people are now confirmed to have died in Rhineland-Palatinate state, with 47 victims in neighbouring North Rhine-Westphalia (NRW) and one in Bavaria.

At least 31 people also died in Belgium, and later torrential rain caused havoc in southern Germany and several neighbouring countries.

"We haven't been to all the houses yet, we must assume that we will find more bodies," said Rhineland Palatinate's regional interior minister Roger Lewentz.

The number of people missing remains unclear, mainly because of disrupted communication networks.

Police in Koblenz said they were still trying to locate 170 people in Rhineland-Palatinate, after managing to get through to several hundred residents who were earlier reported missing.

Graphic showing how torrential rain often causes flooding.

The situation was similar in NRW, where police said they had been able to contact more than 700 residents who were initially unreachable. Several dozen remain missing.

In neighbouring Belgium, the number of people unaccounted for fell from 163 to 70. The country will hold a national day of mourning on Tuesday.

As the scale of the flood disaster became clearer, questions mounted in Germany about whether enough was done to warn residents ahead of time.

Government spokeswoman Martina Fietz said the country's weather warning system and mobile phone app Nina had "worked" but admitted that "our experiences with this disaster show that we need to do more and better".

Armin Schuster, president of the government's civil protection agency (BBK), called on German radio for sirens to be reinstated in more areas as part of the country's disaster warning system.

'Completely inconceivable'

Although meteorological services had forecast torrential rain and flash floods, many residents said they were caught off-guard by rapidly rising waters.

Emergency workers in Germany have been racing to assess damaged buildings, clear debris and restore key services.

The floods caused sweeping power cuts and knocked down telecommunication antennas, preventing residents from receiving warnings in time.

Under Germany's federal system, it is up to the 16 regional states to organise responses to flood alerts and coordinate efforts with the civil protection office and the fire brigade.

Annalena Baerbock, the Green party candidate to replace Angela Merkel as chancellor after elections on September 26, on Monday called for a more centralised approach.

"In my view, the federal government must play a much stronger coordinating role," she told the ARD broadcaster.

But during a visit to the flood-ravaged town of Euskirchen in North Rhine-Westphalia, Interior Minister Horst Seehofer said it would be "completely inconceivable that such a disaster could be dealt with centrally from any one place".

"I believe that we are still in the right position in Germany with our organisation of civil protection and disaster management," he said.

Visiting the flood zone in Rhineland-Palatinate on Sunday, Merkel said lessons should be learnt but sometimes "things happen so quickly that you can't fully escape the force of nature."

Timeline of deadliest floods in Europe in the last 20 years.

Emergency aid

The disaster has catapulted climate change to the top of the agenda in Germany, ahead of September's polls that will mark the end of Merkel's 16 years in power.

Experts say that because a warmer atmosphere holds more water, climate change increases the risk and intensity of flooding.

Merkel's cabinet plans to approve an emergency aid package for flood victims on Wednesday, expected to total around 400 million euros ($470 million). The final bill is likely to be in the billions.

In the German spa town of Bad Neuenahr-Ahrweiler, the search for bodies continued amid mud-covered streets piled high with debris.

"They are still searching. We will find dead people for sure," a resident of the town told AFP, while another said he had witnessed a body being carried away on a cart by soldiers.