Mexican authorities have rescued around 40 migrants who were briefly kidnapped this week while traveling on a bus, officials said Thursday.

Thousands of migrants fleeing violence and poverty in their countries risk abduction and exploitation at the hands of criminal gangs while crossing Mexico on the way to the US border.

These 40-odd people and two drivers were abducted Monday while traveling on a highway in northeastern Mexico.

Nine others from the same group -- which set off from southern Mexico near the Guatemalan border -- were rescued the same day of their abduction after managing to flee, according to officials.

Members of the National Guard were deployed to look for the others and found them Tuesday and Wednesday, national defense secretary Luis Crescencio Sandoval said.

The nine who were first rescued were aged between 18 and 35 years old and from Venezuela and Honduras, according to authorities in the northeastern state of Nuevo Leon.

Ransom demands were made for $1,500 per person, according to the National Confederation of Mexican Transporters.

More than 2,100 migrants were abducted in Mexico last year, according to the National Institute of Migration.

Last month, 35 people, including tourists and migrants, were abducted in northeast Mexico.

They were found aboard five vans guarded by armed men in a desert area.

Early this month, authorities also found 10 Colombian migrants who were allegedly kidnapped while trying to reach the United States.