Two American astronauts completed the installation of docking ports for private shuttles outside the International Space Station (ISS) during a spacewalk.

The goal is to set up a second site where commercial crew vehicles belonging to SpaceX and Boeing can dock and where private astronaut spaceships and NASA cargo flights can dock.

In a statement NASA said the second ISS dock is "a critical step to opening the space station for commercial business to enable the growth of the US commercial space sector and the development of a robust low-Earth orbit economy."

NASA astronauts Nick Hague and Andrew Morgan finished spacewalk after six-hour and 32-minute spacewalk on Wednesday.

The docking port was transported to the station last month on a SpaceX Dragon. It marked the company's 18th commercial cargo resupply service mission to the station.

"It really opens up a variety of opportunities for us. It's really important that we have this additional capability," Kirk Shireman, ISS program manager, said Friday during a briefing about the spacewalk.

NASA's commercial crew partnership with Boeing and SpaceX will restore launches of American astronauts from the United States on US rockets.

The US space agency has partnered with the Russian space program to transport its astronauts to the ISS since the US space shuttle programme ended in 2011.

NASA said last week that plans for the astronauts to install a high-definition television camera during the spacewalk had been scrubbed.

The spacewalk is the 218th in support of station assembly, maintenance and upgrades and the fifth this year. It is the third spacewalk for Hague and the first for Morgan.