San Francisco-based drone deliveries firm Zipline has raised US$25 million in Series B funding to expand its operations across Africa.

Zipline launched in Rwanda last month, enabling blood transfusion clinics across the Western half of the country to place emergency orders by SMS, which are then delivered by one of the company's fleet of 15 drones, called Zips.

The company will soon be making 50-150 emergency flights a day to deliver lifesaving blood to 21 transfusion clinics across the country, and has now raised funding to expand its work in Rwanda to other countries across Africa.

The funding round - which takes Zipline's total raised capital to US$43 million - was led by Visionnaire Ventures and includes investments from Sequoia Capital and Andreessen Horowitz.

Aside from expanding to more countries in Africa and across the world, Zipline also hopes to begin making instant deliveries in the United States within the next six months in collaboration with the White House and the FAA.

"The inability to deliver life saving medicines to the people who need them the most causes millions of preventable deaths each year. Zipline will help solve that problem once and for all," said Zipline CEO Keller Rinaudo.

"We're building an instant delivery system for the world, allowing medicines and other products to be delivered on-demand and at low-cost, anywhere. This new funding will help make that vision possible much sooner."

Visionnaire Ventures co-founder and managing partner Susan Cho said she was looking forward to what the future holds for Zipline and the people that would benefit from its technology.

"Zipline is the best possible combination of social impact and business impact. It's a smart investment that will help save lives," she said.

"While many companies hype drone delivery, Zipline is quietly making it happen," said Alfred Lin, Zipline board member and Sequoia partner.

"Keller is a bold and fearless innovator, and it's been a privilege to be a part of Zipline's remarkable journey from prototype to lifesaving blood deliveries in less than two years. There's much more to come."