Aid workers, residents and medical staff paint a grim picture of the fight to survive as Israeli warplanes pound the Palestinian enclave daily with missiles and the population lives in fear of an invasion at any moment.

Max Gaylard, the UN humanitarian coordinator for the Palestinian territories, said on Friday that "there is a critical emergency in the Gaza Strip right now... By any definition this is a humanitarian crisis and more. Schools are closed, the population is staying home, Gaza is experiencing a food crisis ... hospitals and clinics are absolutely overwhelmed," he said.

"There probably is an air strike every 20 minutes on average, probably intensifying at night," Gaylard said, adding that rockets fired at Israel by Gaza militants "are indiscriminate and expanding in range."

Most houses only get water for one or two hours every five days and electricity is even rarer as Gaza's only power plant has no fuel.

UN agencies say there is no food in the markets. "It is desperate now, the pipes were blown up and there is waste everywhere in the streets -- human, animal, chemical. There was a funeral today and they had to carry the body through that disgusting stench in the street," Beit Hanoun resident Hatem al-Aynun told AFP.