"It accelerated with extreme violence," he told a news briefing in New York by video-conference from ground zero today. "The entire building was shaking violently and I was hanging on to furniture just to stop myself from being thrown around the room and praying that the big concrete pillar in the middle of my office would not break and bring the whole building down on me.
"When it subsided, the central part of the MINUSTAH [UN mission in Haiti] headquarters had collapsed and blocked off access to the outside from my office so all the people like me had to get out of my window and go down three storeys on a ladder, a rather rickety ladder," he said of the quake that had turned much of the hotel into a pile of rubble.
Scores of UN staff were killed or injured and some 150 others are still unaccounted for, including Secretary-General Ban Ki-moon's Special Representative Hédi Annabi, both in the hotel and elsewhere. It must be expected that more bodies will be found as the concrete is moved, said Mr. Wimhurst, adding that he thinks the final overall Haitian toll, which some have estimated at scores of thousands, will be very large.
In another part of town Kim Bolduc, the Deputy Special Representative of the Secretary-General and UN Humanitarian Coordinator in Haiti, was working on the second floor of the main UN Development Programme (UNDP) building when the quake struck.
"It was extremely violent, I didn't even have time to seek cover," she told the same briefing. "I was sitting on my chair and holding on to the table. Everything collapsed around. I saw the wall in front of me opening up with a very large crack and I was just hoping that it would stop. It lasted a long time."
The building was very badly damaged but still standing, while a second UNDP building across the street collapsed completely.
Ms. Bolduc, a Canadian citizen of Vietnamese origin, described heart-rending scenes in the aftermath - "many bodies on the streets, a lot of injured just lying around, houses destroyed, very new and lush buildings just collapsed, the situation is very dire" with people sleeping in the streets.
"People are all in a state of shock, they're not really talking, they are just gathering and sitting together, just waiting for something to happen and fearing aftershocks," she added.
Mr. Wimhurst, also a Canadian, warned of potential anger among the population as their expectations outrun the ability of humanitarian organizations to meet their needs. "It's a hopeless situation," he said. "They want us, they expect us to provide them with help, which is of course what we want to do but we're not in a situation yet where we can do that on a massive scale and, unfortunately, they're slowly getting more angry, I think, and impatient...
"We're all rather aware of the fact that the situation is getting more tense as the poorest people, who do not need so much, are waiting for deliveries, and of course we're trying to do everything we can to get them the help they need. I think tempers might become frayed."
He said he was confident that MINUSTAH had sufficient numbers of military and police in the Port-au-Prince area to handle the situation, but it would bring in reinforcements from others parts of the country if necessary.
"One of the problems is that the national Haitian police are not visible at all, they've simply vanished, they've disappeared so all law and order requirement have to be maintained by us," he added, although he said this was not a criticism of the police since their family members had been killed or injured and their homes destroyed.
MINUSTAH was set up in 2004 after then president Jean-Bertrand Aristide went into exile amid violent unrest. Currently it has more than 9,000 military and police personnel and nearly 2,000 civilian staff.