More than 200 people have been killed and hundreds more are missing after torrential rains triggered severe flooding and mudslides in the city of Mocoa, in southwest Colombia, according to a statement released by the army.

Heavy overnight rainfall caused several rivers to overflow their banks, sending mud and debris crashing on to houses as people slept, and sweeping away vehicles and trees.

Many of the victims did not have enough time to climb on top of their roofs, or seek refuge on higher ground.

"We've declared an emergency in the area so we can help people as best we can," said Colombia's President Juan Manuel Santos, who flew to Mocoa on Saturday to oversee rescue efforts.

He added that 30 percent of monthly rain fell in just one night.

"All of our hearts are with the victims of this tragedy."

An estimated 220 people were still missing, while another 400 were injured, according to the Red Cross.

With no electricity to light Mocoa, authorities were forced to suspend the search for the night.

Mocoa is the capital of Putumayo, near Colombia's border with Ecuador.

Sorrel Aroca, the governor of Putumayo, called the development "an unprecedented tragedy".

There are "hundreds of families we have not yet found and whole neighbourhoods have disappeared", he told a local radio station.

"People do not know what to do ... there were no preparations" made for such a disaster, Hernando Rodriguez, a 69-year-old resident, told the AFP news agency.

Videos and pictures uploaded to Twitter showed wood planks, mud and piles of rubble from destroyed buildings littering the streets of Mocoa.

#TodosConMocoa Este es el panorama de la avalancha que ocurrió en Mocoa, que deja hasta el momento 23 muertos https://t.co/BK5zrz1PFk pic.twitter.com/pT295jucuD — BluRadio Colombia (@BluRadioCo) April 1, 2017

#Galería La tragedia que enluta a Mocoa, en fotos y videos https://t.co/XNJltWcDIu pic.twitter.com/8JOqQiCVZg — Última Hora BluRadio (@UltimaHoraBLU) April 1, 2017

Carlos Ivan Marquez, the director of the national disaster agency, said a crisis group, including military units, police and rescue teams, had been activated to search for the missing people, as well as begin removing hundreds of tonnes of debris.

Simon Uribe, a Mocoa-based filmmaker, told Al Jazeera that people were panicking amid rumours of another avalanche coming.

"You can see people running down the streets, families and individuals trying to call their friends," he said.

"But there is no energy at this moment, there is no fuel and the roads are also blocked, so it is very difficult to get in or out of the city," Uribe added.

"But people are panicking, trying to get out of the city," he said. "People are very anxious."

Colombia has been hit by several deadly landslides in recent months.

Last October, a landslide in the north of the country killed 10 people in October last year.

A month later, another killed nine people in the southwestern rural town of El Tambo, officials said at the time.