At least 92 people have been killed and dozens are missing after catastrophic flooding across Germany and Belgium, which has left several villages cut off and sparked fears that a dam could burst.

Officials have warned that communities in both countries "are still in danger" following Thursday's catastrophe, with German Chancellor Angela Merkel expecting "many" more deaths.

The total number killed in Germany alone has risen to at least 81, according to broadcaster ARD, with communities across the North Rhine-Westphalia and Rhineland-Palatinate states affected.

Among the worst hit areas is Ahrweiler county, south of Cologne, where authorities say around 1,300 people are unaccounted for.

In Belgium, 11 deaths have been reported.

Entire communities lie in ruins after rivers burst their banks and swept through towns and villages - washing away people's homes, flooding basements and causing widespread devastation - following days of torrential rain.

The full extent of the damage in the regions affected remains unclear as many remote areas remain cut off by floodwater and landslides that have made roads impassable.

Mobile phone networks and internet connections are also down in flood-stricken regions, leaving family and friends unable to contact their loved ones.

"I grieve for those who have lost their lives in this disaster," said Ms Merkel, during a visit to Washington.

"We still don't know the number, but it will be many."

On Friday, several houses collapsed in Erfstadt in North Rhine-Westphalia and rescuers were struggling to help families who had returned to their homes despite the warnings, Cologne district government officials said on Facebook.

Authorities in Rhine-Sieg county south of Cologne ordered the evacuation of several villages below the Steinbach reservoir amid fears the dam there could break.

One dam close to the Belgium border, the Rurtalsperre, was flooded overnight while another, the Steinbachtalsperre, is unstable.

The governor of Rhineland-Palatinate state, Malu Dreyer, told the regional parliament: "There are people dead, there are people missing, there are many who are still in danger.

"We have never seen such a disaster. It's really devastating."