A growing throng of Central American migrants resumed their advance towards the US border in southern Mexico today, overwhelming Mexican government attempts to stop them at the border.

Their numbers swelled to about 5000 overnight and at first light they set out walking towards the Mexican town of Tapachula, 10 abreast in a line stretching 1.5km.

Several hundred more already had applied for refugee status in Mexico and an estimated 1500 were still on the Guatemalan side of the Suchiate River, hoping to enter legally.

It was not immediately clear where the additional travellers had materialised from since about 2000 had been gathered on the Mexican side yesterday. But people have been joining and leaving the caravan daily, some moving at their own pace and strung out in a series of columns as they moved across Guatemala.

They marched on through Mexico like a ragtag army of the poor, shouting triumphantly slogans like "Si se pudo!" or "Yes, we could!"

As they passed through Mexican villages on the outskirts of Ciudad Hidalgo, they drew applause, cheers and donations of food and clothing from Mexicans.

- AP