The unmanned SpaceX Falcon-9 rocket, designed to carry supplies to the International Space Station, has exploded minutes after it was launched in Florida, NASA has said.

Sunday's incident occured approximately two and a half minutes after lift-off from Cape Canaveral in the US state.

With more than 5,200 pounds of space station cargo on board, including the first docking port designed for future commercial crew capsules, the 63-metre rocket was SpaceX's 19th Falcon 9 launch since its 2010 debut. 

Pieces of the rocket could be seen falling into the Atlantic.

SpaceX, a private company, was contracted in 2006 by NASA to design and demonstrate a launch system to resupply cargo to the ISS

In a statement, NASA said that the failure was caused by "an overpressure event in the upper stage liquid oxygen tank".

"The astronauts are safe aboard the station [ISS] and have sufficient supplies for the next several months," it said. 

"We will work closely with SpaceX to understand what happened, fix the problem and return to flight."

Gwynne Shotwell, the president and chief operating officer of Spacex, said during a news conference on Sunday that "space transport is a tough business, but we don't anticipate any significant changes for planned launches, including those for the Commercial Crew Programme".

NASA's Commercial Crew Programme relies on commercial spacecraft to launch US astronauts on trips to and from the ISS by 2017.

Francisco Diego, a senior Teaching Fellow at the Department of Physics and Astronomy at University College London, told Al Jazeera that the breakdown can easily be fixed.

"Earlier failures were also fixed, so it is important that we learn from this, and to keep in mind that no human lives were at danger today".

A couple of minutes after the explosion, NASA had tweeted that "space is hard".