Dell was contacted by most of its 80 major clients in the World Trade Centre complex and nearby buildings within 48 hours, the company said.
Dell's US Department of Defence and government customers will get top priority when it comes to shipping replacement systems. They will be followed by health service organisations that lost equipment in the disaster, and commercial customers after that.
"Orders from [affected companies] automatically go to the front of the line," a company spokesman said. "We have set up a dedicated team in our factories to manage these orders."
Hewlett-Packard is shipping systems to affected customers on a similar priority basis. Government and healthcare customers top the company's list, followed by clients in the airline industry and then commercial customers.
HP has established two crisis centres to handle emergency customer requests. One is focused on managing the company's internal processes, as well as the engineering and manufacturing resources needed to respond quickly to customer needs.
The other centre will manage the equipment staging and shipping process, using whatever transport is available, given the current slowdown in air travel.
Two days after the blast HP had received calls from 24 customers requesting everything from server and storage equipment replacements to help with setting up equipment in alternate locations, the company said.
Unisys had "several dozen" customers in the World Trade Centre complex to whom it provided both equipment and services, and to whom it has offered recovery services, said a company spokesman.
For one large public-sector customer headquartered in the complex, Unisys has set up a call centre staffed by 70 people at one of its facilities in New York. It has also helped a large brokerage firm to set up a 150-person trading floor at an alternate location in New Jersey.
Sun Microsystems has established a Sun Support Forum Recovery Assistance Web site providing a range of patches for systems administrators, as well as contact information and discussion forums aimed at helping them quickly recover their computing services based on Sun equipment.