From the Guardian, just now:
The main force of the explosion at the al-Ahli al-Arabi hospital hit a courtyard and car park at the centre of the medical complex, packed with families taking refuge from airstrikes in surrounding neighbourhoods, the Anglican bishop responsible for the compound said.
Hosam Naoum, Anglican Bishop of Jerusalem, also told journalists that in the days before a Gaza hospital was hit by a devastating explosion, Israeli forces had issued three evacuation warnings to its directors, and struck it twice with missiles.
Israel has denied hitting the hospital on Tuesday, saying that the blast was caused by the warhead and propellant of a misfired Islamic Jihad rocket.
Naoum declined to attribute responsibility for the blast, saying that priests were not military investigators, but he condemned the war and called for a ceasefire.
It was crowds fleeing Israeli airstrikes elsewhere in Gaza city who bore the brunt of the blast, he said. “Two of our employees were injured, but the rest there were operations taking place when the blast (hit).”
“At that point in time (of the blast), we know there were thousands of people there,” he said. “They received a warning, there were some bombing and air strikes around the hospital and they fled in (to the hospital compound).”
On Saturday, Sunday and Monday the Israeli authorities contacted hospital staff, mostly by phone, telling them to leave.
“They have the phone numbers of all the directors of the hospitals. So they can either send message or (use) whatever means they have to notify them,” he said.
“We received the two missiles that hit the hospital. We could see and tell that they are from an Israeli strike at the hospital. And then we received the warnings,” he said.
Staff told refugees who crowded into its courtyard about those warnings, but they apparently judged the hospital safer than other options in a city under attack. In the afternoon before hundreds were killed and maimed, they had been singing peace songs to keep up their spirits, Naoum said.
Hospital administrators had warned them about the evacuation notices. “We had a moral obligation,” Naoum said. “We told them it is important you know what is taking place, but they have nowhere to go.”
A crowd of around 5,000 people almost all left after the first warning. But many returned when airstrikes pummelled the neighbourhood, hoping the hospital compound might be a relative haven amid Israel’s blanket evacuation order, that effectively turned all of Gaza city into a potential target.
This does not, of course, give any definitive answers - but it does help explain how comparatively little structural damage could result in a large number of casualties.