(AFP) - Sierra Leone's president issued a desperate appeal for help, a day after flooding ravaged the country's capital, killing more than 300 people and leaving hundreds more missing.

President Ernest Bai Koroma fought back tears and said the devastation was "overwhelming us", as he toured Regent, one of the worst-hit areas.

"Entire communities have been wiped out," Koroma said Tuesday. "We need urgent support now."

As the city began to bury its dead, foreign governments began mobilising aid, with Israel pledging to provide clean water, medicines, blankets and other essentials.

The UN said it was evaluating humanitarian needs in the country and that "contingency plans are being put in place to mitigate any potential outbreak of waterborne diseases such as cholera, typhoid and diarrhea", according to spokesman Stephane Dujarric.

He noted that the International Organization for Migration had released $150,000 in emergency funds.

Heavy rains streaming down a hill in Regent triggered a landslide that engulfed homes three or four storeys high, many of them built illegally.

Koroma toured Regent's Connaught hospital and central morgue, which has been overwhelmed by bodies.

The government of Sierra Leone, one of the poorest countries in the world, has promised relief to more than 3,000 people left homeless, opening an emergency response centre in Regent.

The Red Cross said 600 people were still missing.

Red Cross official Nasir Khan told AFP the death toll was around 300 on Tuesday evening, but a separate morgue assessment put the figure at 400.

Sulaiman Zaino Parker, an official with Freetown's city council, said 150 burials took place on Tuesday evening and that many would be laid to rest in graves alongside victims of the country's last humanitarian disaster, the Ebola crisis, in nearby Waterloo.

"We have started burying some of the mutilated and decomposed bodies. All the corpses will be given a dignified burial with Muslim and Christian prayers," Parker said.

The graves would be specially marked for future identification, he added.

- 'Sprawling shacks all gone' -

The Red Cross said it was struggling to excavate families buried deep in the mud that engulfed their homes, though several bodies were pulled up by diggers in Regent on Tuesday, according to an AFP journalist at the scene.

"We are racing against time, more flooding and the risk of disease to help these affected communities survive and cope with their loss," said Abu Bakarr Tarawallie, another Red Cross official.

Regent residents told AFP that boulders and rocks had killed many in their homes, while a hill partially collapsed as floodwaters streamed down the slopes.

One resident, Abubakar Mansaray, said it took just two minutes for the mudslide to suffocate families in the darkness.

"Many unfinished buildings were at the hilltop, with those sprawling shacks all gone," he told AFP.

Dozens of injured survivors were receiving treatment, the Red Cross's Tarawallie said, but some residents said they had received no assistance by Tuesday morning.

- Stagnant water -

Three days of torrential rain culminated on Monday in the Regent mudslide and massive flooding elsewhere in the city, one of the world's wettest urban areas.

The city's drainage system was quickly overwhelmed, leaving stagnant water pooling in some areas while creating dangerous waterways that churned down steep streets.

Society 4 Climate Change Communication (S4CCC), a local environment group, called the tragedy a "wake-up call".

"Man-made activity meets climate-change head on, a predictable event now made tragically real," the group said in a widely shared blog post.

Deforestation, a lack of urban planning and vulnerability to climate change had all played a part, they said.

Sierra Leone's meteorological department issued no warning ahead of the torrential rains -- which might have allowed for swifter evacuations from the disaster zones.

At the city's military hospital, community health officer Wilberforce Mohammed Rogers said he had treated several children with multiple injuries, including a six-month-old baby. Many had lost their parents, Rogers said.

Deputy health minister Madina Rahman said contaminated water meant the city was now bracing for a possible cholera outbreak.

- Annual ordeal -

Freetown is hit each year by flooding during several months of rain, and in 2015 bad weather killed 10 people and left thousands homeless.

Sierra Leone was one of three west African nations hit by an outbreak of Ebola virus in 2014 that left more than 4,000 people dead in the country, and it has struggled to revive its economy since the crisis.

The country ranked 179th out of 188 countries on the UN Development Programme's 2016 Human Development Index, a basket of data combining life expectancy, education and income and other factors.

© Agence France-Presse