A pregnant Swedish base jumper has died on what was to be her last jump when her parachute failed to open, media reports say.

Wioletta Roslan, 37, was four months' pregnant and had decided to give up the sport she loved since taking up skydiving at 19, the Daily Mail reported.

But on her last base (buildings, antennas, spans and earth) jump in the Lauterbrunnen valley near Stechelberg, Switzerland, with her partner Aleksander Domalewski on Sunday, her parachute did not open, reports said.

She struggled with it but when she could not release the parachute, she "gave up and spread her arms", her mother Halina Zaniewska-Pettersson told German-language Swiss daily Blick.

Domalewski could only watch in horror as his girlfriend plunged 300 metres to her death, the Mail reported.

"I am very sad and shocked," 68-year-old Zaniewska-Pettersson told Blick.

"I have repeatedly asked them to stop jumping. But she wanted to keep going.

"For me it is a double loss. I had become a grandmother. She was a true adventurer, travelling to France, Italy, Australia, New Zealand, Thailand, America. Often they took me. She was ... full of life."

In a 2008 Swiss television documentary, Roslan, who worked as inspector on oil rigs, said she could not imagine a life without base jumping, where parachutists jump from cliffs, bridges or buildings.

She was also a wingwalker, an extreme sport where people are strapped to the top wing of a flying vintage plane.

"I feel alive when I jump. I find normal life boring," Blick reported Roslan as saying in the documentary.

"We have a certain amount of time on this earth. And when the sun goes down, then the [game is over]."