Unknown assailants have abducted the daughter of the man who heads Colombia's National Protection Unit (UNP), the force charged with guarding people at risk of kidnapping or assassination.

Daniela Mora, 11, the daughter of UNP chief Diego Mora, was abducted as she left school in Cucuta, a city on the Venezuelan border, authorities said.

An armoured vehicle driving her home was intercepted by the kidnappers in circumstances which remain unclear, Colombian media reported.

"The government is doing everything possible to get her back," said president Juan Manuel Santos, after national security officials held an emergency meeting in Cucuta.

The UNP is charged with protecting about 7,500 people deemed to be threatened by Colombia's five-decade civil war, a conflict rife with kidnappings and assassinations.

Created in 2011, the agency spends $600,000 a day guarding politicians, journalists, activists and others deemed to be at risk.

National police chief Rodolfo Palomino said the motive for the girl's kidnapping appeared to be "purely economic, for extortion".

But interior minister Juan Fernando Cristo said officials were not ruling out any possibility.

Defence minister Juan Carlos Pinzon announced a reward of $96,000 for information leading to the girl's recovery, increased from an initial amount of $38,000.

The local unit of the UN Office of the High Commissioner for Human Rights condemned the "despicable practice" of kidnapping, saying it "must end immediately".

Cucuta, a northern city of 650,000 people, suffers rampant crime, drug trafficking and smuggling.

The area is a bastion for the country's two largest rebel groups, the Revolutionary Armed Forces of Colombia (FARC) and National Liberation Army (ELN).

AFP