The bishop of the Colombian city scourged by landslides on Saturday has described a "complex and chaotic situation", and appealed for humanitarian aid for the city's inhabitants.

Landslides swept over Mocoa in the early hours of April 1 when the three rivers that flow through the city overflowed after torrential rainfall. At least 254 people have died in the natural disaster, and hundreds were injured.

Bishop Luis Albeiro Maldonado Monsalve of Mocoa-Sibundoy has issued "a call for solidarity for everyone to join together in this difficult moment, to look toward this region in so great of need."

In a statement posted on the website of the Colombian bishops' conference, Bishop Maldonado appealed for aid, noting that water, food, blankets, and mattresses are urgently required.

Colombia's bishops also called for prayers for those who died and those left homeless by the flooding. The Church has formed a committee to care for, listen to, and accompany the victims of the landslides.

Aid is being delivered by helicopter because roads to Mocoa have been battered or blocked by the disaster.

Before his Angelus address on Sunday, Pope Francis said he was deeply saddened by the tragedy.

"I pray for the victims and assure you of my closeness to those who mourn the death of their loved ones, and I thank all those who are working to bring succour."