The Associated Press said on Saturday it was "shocked and horrified" by an Israeli air strike that destroyed a building housing the US news agency's Gaza bureau and those of other international news media.

"This is an incredibly disturbing development. We narrowly avoided a terrible loss of life," AP President and CEO Gary Pruitt said in a statement about the attack on the building, which also housed Qatar-based Al Jazeera.

A dozen AP journalists and freelancers had been in the building but were able to evacuate, Pruitt said.

The White House, which has kept a relatively low profile on the Israeli-Palestinian flareup, said on Saturday it has cautioned Israel about the importance of protecting independent media.

"We have communicated directly to the Israelis that ensuring the safety and security of journalists and independent media is a paramount responsibility," White House press secretary Jen Psaki tweeted.

Israeli defense officials said the building housed not only news bureaus but offices of Hamas militants.

AFP journalists watched the building collapse after the air strike, sending up a huge cloud of dust and debris.

Al Jazeera television was among the tenants of the building.

Walid Al Omari, that news agency's Jerusalem bureau chief, vowed the network will not be silenced.

"Clearly there is a decision not only to sow destruction and killing, but also to silence those who broadcast it," he told AFP, adding in an on-air interview shortly afterward that "this is impossible".

Pruitt, in his statement, said, "The world will know less about what is happening in Gaza because of what happened today."

The New York-based Committee to Protect Journalists also demanded an explanation from the Israeli government.

"This latest attack on a building long known by Israel to house international media raises the specter that the Israel Defence Forces is deliberately targeting media facilities in order to disrupt coverage of the human suffering in Gaza," said CPJ Executive Director Joel Simon.

"We demand that the Israeli government provide a detailed and documented justification for this military attack on a civilian facility given the possible violation of international humanitarian law," Simon said.