HOULA, Syria -- With fighting intensifying between the Syrian military and armed rebels seeking to topple President Bashar Assad, the number of people who’ve fled their homes for shelter elsewhere has skyrocketed, leaving humanitarian aid agencies and residents scrambling to provide food and water to an ever-growing population of the displaced that likely numbers more than a half million.

With summer temperatures regularly rising above 100 degrees, the crisis is particularly acute in Homs province, where fighting has all but emptied many towns and villages of residents.

“There’s no water to drink and it’s very hot,” one woman said in the rebel-held city of Houla as she took advantage of a lull in violence to load some belongings from her home onto a flatbed truck before returning to a nearby refugee camp, departing so quickly that a reporter couldn’t get her name.

Houla, composed of five districts that total more than 100,000 residents, remains under siege after shelling and fighting reduced parts of the city to rubble last month. A massacre of women and children that took 80 lives then prompted those who hadn’t lost their homes to flee.

Houla is surrounded by the Syrian army and checkpoints manned by pro-government militia known as shabiha. The government has cut off the municipal water supply and those who remain in the city rely on wells for water. Most food and other goods that arrive here make their way across bumpy back roads largely under the protection of the Free Syrian Army, the rebel group that controls much of the countryside.

Others have fled the city to areas outside Houla that are relatively safe. In Al Bourj, a village adjacent to Houla, about 900 people have occupied a pair of schools and others are sharing houses. Al Bourj has no running water either, however, and refugees lined up outside the schools to fill buckets and canisters from a tanker pulled by a tractor.

Local leaders estimate that Al Bourj’s population has more than doubled. In nearby Taldo, the population has tripled, Abdel Nasser al Barra said. “There are about 4,500 refugees here,” he said.

Just how many Syrians the fighting has displaced is unknown. The United Nations estimated at the end of May that at least 500,000 had fled their homes, and the number is surely higher now, given the increase in violence as the rebels press to push the military out of towns.

Three days after the massacre May 25 in Houla, for example, rebel fighters pushed the military out of several positions it had held in the city. The army’s response was more shelling.

“Thirty-five people have been killed in the last month,” said Abu Ali, a member of the local Revolutionary Command Council, which essentially has become the civil wing of the Free Syrian Army. “Some of them died from treatable wounds.”

Abu Ali said that seven of those killed were fighters and the rest civilians.

Traveling through the province of Homs, it’s clear that the fighting has rendered many urban areas uninhabitable, forcing residents to seek shelter elsewhere. The cities of Qusayr, Talbiseh and Rastan are almost empty. The population of those areas alone would account for about 150,000 displaced people. That’s before taking into consideration the city of Homs itself, Syria’s third largest, with more than 1 million residents. Months of fighting there have emptied a number of neighborhoods of everyone but the rebels.