American astronaut Jeff Williams, 58, broke his retired NASA colleague Scott Kelly's record for the most cumulative days in space Wednesday, the US space agency said.

Williams, an accomplished spacewalker, surpassed Kelly's record of 520 days on August 24.

By the time Williams returns to Earth on September 6, he will have tallied 534 days in space over his career, more than any American astronaut.

Russia's Gennady Padalka still holds the record for the person with the most cumulative days in space, with 879.

Williams first blasted to space aboard the shuttle Atlantis in 2000.

He returned to the International Space Station in 2006 when the space station was far smaller, with just two modules and three crew members. Today it is staffed by six astronauts and cosmonauts and spans the size of a football field.

"In 2009 and 2010, he served as a flight engineer on Expedition 21 and commanded Expedition 22, when the Tranquility module and cupola were added to the station," NASA said.

On his current mission, Williams is making use of his spacewalking expertise.

He stepped out on his fourth career spacewalk August 19 to help install a parking spot for future space taxis, along with NASA flight engineer Kate Rubins.

He and Rubins will do one more spacewalk together on September 1 to move a piece of equipment outside the International Space Station, which orbits the Earth.

Williams is a native of Wisconsin and is married with two grown sons and three grandchildren, according to his NASA bio.