Tripoli (AFP) - Half a million children are in "immediate danger" in Libya's capital Tripoli due to fighting, the United Nations children's fund UNICEF said on Monday.

Clashes that broke out between rival militias in late August had killed at least 115 people and wounded nearly 400 by Saturday night, according to Libya's health ministry.

UNICEF said more than 1,200 families were displaced in the past 48 hours as the clashes intensified in southern Tripoli before pausing on Monday.

That put the total number of people displaced by the recent fighting at over 25,000, half of whom were children, it said.

The UN agency's Middle East and North Africa director, Geert Cappelaere, said children were paying a "heavy toll" and were increasingly being recruited by armed groups.

"We see children being prevented from going to school, we see children not having the vaccination that they urgently need," he said.

Those whose parents came to Libya with the hope of migrating to Europe by sea suffered doubly, said Cappelaere.

"They are already facing dire living conditions, many of them are held in detention," a situation made worse by "the violence that is happening today," he said.

UNICEF also said schools are increasingly being used to shelter displaced families, which is likely to delay the start of the academic year beyond October 3.

It said residents are facing food, power and water shortages, adding that the clashes had exacerbated the plight of migrants.

"Hundreds of detained refugees and migrants, including children, were forced to move because of violence. Others are stranded in centres in dire conditions", Cappelaere said.

Despite a UN-brokered ceasefire on September 4, fighting broke out again last week in southern districts of the capital.

The clashes have pitted armed groups from Tarhuna and Misrata against Tripoli militias nominally controlled by Libya's UN-backed unity government.

The Libyan capital has been at the centre of a battle for influence between armed groups since dictator Moamer Kadhafi was ousted in a NATO-backed 2011 uprising.

The country's unity government has struggled to exert its control in the face of a multitude of militias and a rival administration based in eastern Libya.