A commercial spacecraft operated by US space company SpaceX blasted off Friday for its third cargo resupply mission to the International Space Station (ISS), NASA TV showed.

The unmanned Dragon spacecraft was launched aboard a Falcon 9 rocket at 3:25 p.m. EDT (1925 GMT) from the Cape Canaveral Air Force Station in Florida.

"Liftoff!" NASA said in its launch blog. "Dragon is on the way to the International Space Station!"

The spacecraft carried nearly 5,000 pounds (about 2,268 kg) of supplies and payloads, including materials to support more than 150 scientific experiments this year.

The mission was also used to test the so-called "soft landing" of Falcon 9's first stage, which is equipped with four landing legs.

According to the California-based company, soon after the first stage shut down and separated from the upper stage, it should relight some of its engines for a braking maneuver. Then, the stage should ignite an engine again just above the Atlantic Ocean for a landing burn.

SpaceX gave the chance of success at just 30 to 40 percent, and at a post-launch press conference, SpaceX CEO Elon Musk said that he "wouldn't give it high odds" for successful soft landing due to the rough seas and experimental nature of the test.

However, he later wrote on Twitter that "data upload from tracking plane shows landing in Atlantic was good!"

"Flight computers continued transmitting for 8 seconds after reaching the water. Stopped when booster went horizontal," he said.

Several boats, said Musk, are now heading to the landing area, but actual recovery may be an issue because of the heavy seas.

"Eventually, SpaceX hopes to land the first stage on land," the company said, adding the test "represents an exciting effort toward someday developing a reusable rocket."

If everything goes as planned, Dragon will arrive at the station Sunday, when it will be grappled and berthed to the orbiting lab for an expected four-week visit. It is scheduled to depart the space station May 18 for a parachute-assisted splashdown off the coast of California.

The launch is proceeding despite the failure last Friday of a backup computer called multiplexer-demultiplexer (MDM) that provides commands to some space station systems, including the external cooling system and the Mobile Transporter rail car on the S0 truss of the station.

This is the third of at least 12 missions to the space station that SpaceX will fly for US space agency NASA under a 1.6-billion-US dollar Commercial Resupply Services contract.

Besides SpaceX, NASA has also signed a deal with another private company called Orbital Sciences Corp. to supply cargo to the space station.