Since July, floods have killed 576 people and affected more than 1.9 million, according to the latest figures from the UN Office for the Coordination of Humanitarian Affairs (OCHA) this month -- more than 10 percent of the Central African nation's population.
The waters of the Chari, which join the tributary Logone in N'Djamena "keep rising" and on Wednesday reached a record 8.18 metres, said Prime Minister Allah-Maye Halina at an emergency meeting attended by army general staff.
While soldiers had already been deployed to construct dams and barriers with sacks of earth to slow the spread of the water toward residential areas, Halina called on businesses to "mobilise their machinery" and build embankments.
"Every minute is precious," he warned.
One neighbourhood of N'Djamena built in a flood zone in the 1970s and 80s, a period marked by drought, was already being hit by waters from the Chari and Logone, according to an AFP reporter at the scene.
The last record for the Chari was 8.14 metres, set in November 2022, when the country saw its heaviest and deadliest rainfall that resulted in the highest death since the 1960s, according to OCHA.
Since the beginning of the summer, the Lac province has been the hardest hit by floods but no region has been spared, with all 23 of the Chad's provinces being affected.
More than 217,000 homes have been destroyed, 432,000 hectares of fields ravaged and 72,000 livestock killed, OCHA said.
The downpours are "a stark reminder of the growing impact of climate change", which have hit swathes of the African continent, killing more than 1,500 people and displacing at least 1.2 million across Burkina Faso, Cameroon, Chad, Mali, Nigeria and neighbouring countries, according to late September figures from the UN's International Organization for Migration.
UN officials warned early in September about the impact of torrential rains in West and Central Africa, including Chad, calling for "immediate action and adequate funding" in the face of the "climate crisis".
An estimated $129 million is needed to respond to the crisis in Chad alone, the OCHA said.