KINSHASA -- At least 120 people have been killed in the Democratic Republic of Congo capital Kinshasa after heavy rains unleashed floods and caused landslides, a government document seen by Reuters showed on Tuesday.

Entire neighbourhoods were flooded with muddy water, and houses and roads ripped apart by sinkholes, including the N1 highway that connects Kinshasa to the chief sea port of Matadi.

The prime minister's office said in a statement that the N1 could be closed for 3-4 days.

The death toll was compiled by the General Management of Migration, a part of the interior ministry.

The toll may rise. Health minister Jean-Jacques Mbungani Mbanda told Reuters the ministry had counted 141 dead but that the number needed to be cross-checked with other departments.

Images posted on Twitter by Congo's government spokesman Patrick Muyaya showed a major road that appeared to have subsided into a deep chasm, with crowds staring at the damage.

"On the National Road 1 there is a big hole. Only pedestrians can pass. We do not understand how the water cut the road," said local resident Gabriel Mbikolo.

Once a fishing village on the banks of the Congo river, Kinshasa has grown into one of Africa's largest megacities with a population of around 15 million.

Poorly regulated rapid urbanization has made the city increasingly vulnerable to flash floods after intense rains, which have become more frequent due to climate change.

At least 39 people died in Kinshasa in 2019 when torrential rain flooded low-lying districts and some buildings and roads collapsed.

In addition to damaged infrastructure, each day of flooding costs households a combined $1.2 million due to the large-scale transport disruption, according to a 2020 World Bank paper.