The hopes to have all 9,000 of its servers in its Houston datacentre back online following a blast that shut down the facility on Saturday afternoon.

When firefighters arrived around 5 pm, they could see "light smoke" at the Planet datacentre - the aftermath of an explosion in a network gear room that hit with enough force to move walls.

Sprinklers quickly doused whatever flames erupted from the blast, and the fire was attributed to an electrical problem with a transformer, according to a Houston Fire Department spokeswoman. There were no injuries.

Although the datacentre says it has power systems that "are designed to run uninterrupted" and a "fully redundant network operations centre" with diesel generators, the electrical problem exposed an apparent Achilles' heel in its business continuity planning.

Firefighters told datacentre workers to turn off all the power, according Planet spokeswoman Yvonne Donaldson. That meant the servers, even though they weren't damaged, were offline.

Approximately 6,000 of the affected servers were returned to service early this morning. Another 3,000 were due to return online by tonight, the company said. The Planet staff provided updates on the restoration on its customer forum site, including a message from CEO and chairman Douglas Erwin, wrote that some servers will be relying on generator power for a week until normal utility connections are restored.

The Planet operates more than 40,000 servers at multiple datacentres and hosts more than 3 million websites.

While Planet datacentre staff worked to restore service, users - many of them small business owners - wrote of their frustrations over the outage on forum posts.

Questions about the datacentre's backup capabilities were raised, as well. One person, flynnibus, wrote: "You shouldn't put all your money into one bank - and you shouldn't put all your servers in one DC [datacentre] if you want to be truly resilient."