Christian aid organisation World Vision has called on the US government to protect migrant children and families and condemned threats to withhold aid to their home countries.

A migrant 'caravan' estimated at 7,000 to 10,000 Central Americans fleeing violence and poverty in their homelands is in southern Mexico, inching towards the distant US border. President Trump, fighting to retain Republican control of the Senate and House of Representatives next month, has described this as a 'national emergency'.

'Guatemala, Honduras and El Salvador were not able to do the job of stopping people from leaving their country and coming illegally to the US. We will now begin cutting off, or substantially reducing, the massive foreign aid routinely given to them,' Trump wrote in a series of Twitter posts. 'Remember the Midterms!' he tweeted.

World Vision said in a statement: 'Sadly, the countries of the Northern Triangle – El Salvador, Guatemala, and Honduras – continue to be plagued by endemic levels of crime and violence that have made many communities extremely dangerous, especially for children.'

It said: 'Because World Vision works in hundreds of communities in Latin America, we understand the violence and sense of hopelessness that is driving families to leave their homes. As Christians, we are called to love and serve the most vulnerable among us, to welcome the stranger, and to show hospitality to those in need (Matthew 25:35).'

World Vision does not encourage families to migrate, it said, but was 'deeply concerned for the health and safety of children and families fleeing the violence in Honduras and urge that measures are taken to appropriately care for these children while they are on the move. Our hope is that by addressing the root causes of poverty and violence across Latin America, we can prevent unsafe migration from happening in the future and protect children from the violence and trauma they may encounter at home or along the way.'

It urged the US government to address the 'root causes' of migration through foreign assistance, which 'should not be used as a tool to penalize the home countries of migrants, but should instead remain focused on improving the lives of the most vulnerable so that children and their families may safely remain home'.

The caravan is still a long way – more than 1,100 miles (1,800 km) – from the US border. Mexico hopes to disperse the convoy long before it can reach the border using bureaucratic procedures, telling migrants to register with authorities in order to submit applications for asylum in Mexico.

Additional reporting by Reuters.