Thousands flee Gaza's north as Israeli troops and Hamas battle

Thousands of Palestinian civilians trudged in a forlorn procession out of the north of Gaza on Wednesday seeking refuge from Israeli air strikes and fierce ground fighting between Israeli troops and Hamas militants.

The exodus took place in a four-hour window of opportunity announced by Israel, which has told residents to evacuate the north encircled by its armoured forces or risk being trapped in the violence.

But the central and southern parts of the small, besieged Palestinian enclave also came under fire again as the war between its Islamist Hamas rulers and Israel entered its second month.

Palestinian health officials said an air strike that hit houses in the Nusseirat refugee camp killed 18 people on Wednesday morning. In Khan Younis, six people, including a young girl, were killed in an air strike.

"Civilians, all of them civilians. An old woman, an old man and there are others still missing under the rubble," said a witness, Mohammed Abu Daqa.

Gaza City, the Hamas militant group's main bastion in the territory, is now surrounded by Israeli forces. The military said troops have advanced to the heart of the city, while Hamas says its fighters have inflicted heavy losses.

Chief Israeli military spokesperson Rear Admiral Daniel Hagari said combat engineers were using explosive devices to destroy a Hamas tunnel network that stretches for hundreds of kilometres beneath Gaza.