Yet for many foreigners in Nairobi there is already a sense that the city will bounce back.
A decade ago in Nairobi, there were few options for a family weekend day out that would allow for shopping, lunch, somewhere for the kids to play and maybe later a movie.
Recently, however, a dozen large Western-style malls have sprung up. They are busiest on Saturday mornings when each is full of local shoppers and store staff and they sport large numbers of expatriates who call the Kenyan capital home.
Since Islamist attackers stormed the most high-profile of those shopping centers on Saturday, the fear of further attacks and of a lack of trust in security arrangements is likely to keep customers away, at least in the short term.
In the longer term it is bringing sharp new appraisals about a city considered the most foreigner-friendly in Africa. Nairobi is home to hundreds of regional corporate offices and is relatively choc-a-block with American and European students and NGOs. Many expatriates avail themselves of a comfortable standard of living in a place once quaintly known as the Green City in the Sun.
“How can any of us sit in any of these shopping centers any more and not think that it can happen again,” asks Bridget Allison, a British media producer who has lived in Nairobi for close to a decade.
“My friends in the UK used to look on my life in Kenya with envy, but now they’re looking at me like I’m mad to want to live here, and that if you do, you’re being very selfish to put your family in these kinds of risks,” she says.
Life in Nairobi had for long carried the features inherent in places where vast disparities in wealth raised risks of robberies, car-jackings, and home invasions.
Homes are hidden behind high walls, often topped with razor wire. Home alarm systems and lockable safe rooms are must-haves in many houses rented to foreigners. Restaurants popular with expats sit out of sight of the street outside.
Despite this, the majority of overseas residents would say the city’s previous nickname of "Nairobbery" is now outdated, and that the benefits of living here have outweighed the risks.
The threats have, however, taken on a much more sinister and serious edge since Al Qaeda-allied Islamists expanded in Somalia, and then threatened to strike Nairobi when Kenyan forces invaded their neighbor to battle the militants.
Since then, amid repeated warnings of a jihadi strike planned for the Kenyan capital, there has been an apparent increase in security at many shopping centers, hotels and office buildings in the last few years here.
Uniformed but unarmed and poorly-paid guards from private security companies staff doors and run handheld metal detectors over people entering these buildings, although most would agree that these checks are cursory at best.
“It seems that people in charge got negligent as time moved on after the initial warnings, and now the Westgate attack was a brutal wake-up call,” says Michael Franz, a German aid worker.
“I’m not sure whether armed guards and better security checkpoints would have done much good against coordinated teams of probably battle-hardened fighters with heavy weapons, but it might have, and the question should be asked,” he adds.
The repeated threat alerts featuring the Westgate shopping center had already changed Mr. Franz’s daily life in Nairobi, he says.
“I made my decision to minimize my visits to Westgate. I felt way more comfortable at other malls that seemed less attractive [as terrorists’ targets], and also much better in terms of security.”
The Westgate siege may also have an impact on international companies that do business with Kenyan firms, says Geraldine O’Keeffe, an Irish internet technology provider based in Nairobi.
“The effect of this attack is not just where am I going to do my shopping or have my Sunday brunch now that I don’t feel safe in this mall or that mall,” she says.
“I’ve had clients all over the world, in Vanuatu, in Cambodia, in Burma, calling me up to check I’m OK, but also to check that as a supplier, I’m still going to be able to deliver," she says. “People are going to question whether doing business with a Kenyan company will be reliable if there are issues like this.”
At the same time, some experienced international business and corporate types are saying they will take the mall assault in stride.
Jules Lambert, a British petrochemicals entrepreneur who’s lived in Nigeria and South Africa and will soon move to Kenya, says for example that, "bad stuff like this happens all over the world."
"I am about to invest a lot of money in an oil and gas project in Kenya, and this attack, while horrific, does not put me off or make me worry excessively about security," he says.
Nor is Kenya a stranger to terrorist attacks. In 1998, Al Qaeda’s first major international strike was the twin bombings of the US embassies in Nairobi and Dar es Salaam, Tanzania, killing more than 200 people including 12 Americans.
Four years later, jihadists trained in Somalia tried to down an Israeli jet with a rocket-propelled grenade, and they crashed a truck full of explosives into a Kenyan hotel on the Indian Ocean, leaving 13 people dead.
The country has recovered from both attacks. There is already here a sense that, while mourning the 63 people who died in the mall assault, Kenya will again bounce back.
“In the short-term, yes, maybe we’ll decide not to do our grocery shopping at peak times,” says Jehan Balba, an American aid worker who lived in South Sudan before moving with her husband, a photographer, to Kenya in January.
“But as soon as it’s clear that this was a one off, I think it’ll go back to how it was before. There have been attacks here before, but people didn’t desert the place. I can’t see that they will now.”