President Juan Manuel Santos said the authorities do not know how many people are still missing.
Heavy rains caused the river Liboriana, in the town of Salgar, to burst its banks, triggering the landslide.
Much of the village of Santa Margarita, south-west of the provincial capital, Medellin, was swept away when the disaster hit early on Monday.
Rescue teams and residents have got together to dig through rouble in the hope of finding survivors.
After visiting the scene of the disaster, Mr Santos declared a state of emergency and promised to rebuild the houses.
"We cannot bring the dead back, which we regret deeply, and we will support the families (of the victims)," said Mr Santos earlier.
"But we have to move on from this tragedy, and look ahead with courage and fortitude."
"The priority now is the hospital," said the president.
Earlier on Monday, gas and electricity services in the town were suspended as a precautionary measure.
The Colombian Air Force and police have sent helicopters to the area. More than 160 soldiers are working in the emergency effort.
Some 100 people have been evacuated from high-risk areas.
Local official Zulma Osorio spoke of a "tragedy of enormous proportions".
Mud, rocks and tree trunks destroyed many houses in poor neighbourhoods close to the river.
Resident Jorge Quintero described his ordeal when the landslide hit the village: "When I felt my house shaking we got out, my family and me. When we got out, we were stuck in the middle of the landslide, it was coming from both sides and we were in the middle.
"I said to my wife, let's hold each other and hope that God saves us and I know he gave us his hand because here we are, alive, still frightened, but still alive."
More rain is expected in the are in the next few days.

All 42 of its member clubs are expected to take strict disciplinary measures against fans who indulge in anti-social behaviour during matches.
The updated guidance, which comes into force immediately, states that home clubs are responsible for "good order and security".
Clubs are also urged to step up efforts to identify culprits.
Under the previous rules, clubs could argue that they had taken all practical steps to deter misbehaviour inside their stadiums.
Now they must been seen to actively pursue cases and take "appropriate" action against the perpetrators.
In June, following disorder at the Scottish Cup final, Justice Secretary Michael Matheson called for "a transparent and robust scheme" to prevent and deal with unacceptable conduct.
He went on to warn: "The Scottish government is prepared to act if Scottish football isn't."
On the rule changes, SPFL chief executive Neil Doncaster said: "The SPFL and its member clubs are committed to preventing and to addressing unacceptable conduct where it arises, to ensure our stadiums are friendly, welcoming and safe environments where all supporters can enjoy Scottish football.
"This ongoing work includes this updated guidance for clubs which sets out the reasonably practicable measures that member clubs can take to address this issue and to identify and sanction those who engage in unacceptable conduct.
"It has been fully consulted on with all 42 clubs, the Scottish FA and the Scottish Government and, indeed, dialogue continues with the Government on a number of further measures which will be discussed early this year."

10 September 2016 Last updated at 18:36 BST
The house of Pietro's owner collapsed as a result of the quake. The cat was taken to a veterinary clinic and is said to be in a critical condition.
He was found when his owners returned to the house to get some belongings.
Nearly 300 people died in August's magnitude-6.2 earthquake.
Read more
Tales of survival
Before and after images show destruction
More than 50 people have been killed in a landslide in Antioquia province in north-west Colombia, officials say.
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The Scottish Professional Football League has issued new regulations aimed at tackling supporter misconduct.
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A cat has been rescued from the rubble of a house 16 days after an earthquake hit the Italian city of Amatrice.