LONDON (AP) — Britain and Sierra Leone are appealing for more help to slow the biggest ever Ebola outbreak — and are proposing a new type of clinic to do that.

At a London conference on Thursday, officials are expected to announce plans to build up to 1,000 makeshift Ebola clinics in Sierra Leone. The new clinics will offer little, if any, treatment, but they will get sick people out of their homes, away from their families and hopefully slow the infection rate.

Only a fraction of Ebola patients are now in treatment centers.

"If we don't do anything, we'll just be watching people die," World Health Organization spokeswoman Dr. Margaret Harris said in Sierra Leone.

Sierra Leone is one of the hardest-hit countries in the Ebola outbreak in West Africa, which is believed to have killed more than 3,300 people and infected at least twice as many.

Experts say the disease will continue to spread rapidly unless at least 70 percent of people who are infected are isolated and prevented from infecting other people. Dozens of Ebola treatment centers have been promised, but they could take weeks or even months to go up.

The basic care centers, however, could be put up in as little as a week's time, said Manuel Fontaine, the West Africa regional director for the U.N. Children's Fund, which would help equip them.

"It's not one or the other," Fontaine said. "What we're saying is the care centers need to move fast but that shouldn't be an excuse to slow down the ETUs (Ebola Treatment Units)."

Experts are turning to these imperfect solutions because the scale of the Ebola outbreak is overwhelming the traditional response methods tried so far.

Save the Children noted Thursday that Ebola is spreading at a "terrifying rate," estimating that in recent days five people were becoming infected every hour in Sierra Leone alone. That figure is based on both confirmed cases and an estimate of how many cases are not being reported.

"We need to try different things because of the scale of this outbreak," said Brice de la Vingne, director of operations for Doctors Without Borders.

"We've used these kinds of basic tents in past catastrophes but never for Ebola," he explained. "But right now we're screaming for more isolation centers so patients don't infect their communities."

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AP Writer Sarah DiLorenzo reported from Dakar, Senegal.