One of the last surviving architects of the Soviet space programme that put Yuri Gagarin into orbit half a century ago died on Wednesday, officials said. He was 99.

Boris Chertok, who helped design the country's first ballistic missiles, was a close colleague of the Soviet rocket design genius Sergei Korolyov who is widely credited for giving the USSR the lead in the early space race.

"He died today at 7.40 am in the morning," spokesman for Russian rocket-builder Energia told AFP.

Chertok was considered one of the last living legends of the early years of human space flight who made Gagarin's trailblazing 1961 flight a reality.

"He was the last of the 'Mohicans'," Mikhail Turchin, Chertok's assistant since 1965, told AFP. "He was Korolyov's last deputy."

Chertok was a close associate of Korolyov, considered the father of the Soviet space programme, and designed the country's first satellites and spacecraft including the spaceship that took Gagarin around the globe on his historic 108-minute journey.

Chertok started his career at Energia in 1947 and stayed with the company until his last days, working as its chief scientific consultant.

He died just two and a half months shy of his 100th birthday.

"We were preparing to celebrate his birthday," the Energia spokesman said, adding that he impressed everyone around him with clarity of thought, even if he needed assistance getting to work in his last years.

Colleagues spoke warmly of him, saying his role in the country's space programme could not be overestimated.

"Boris Chertok is the thread that connects our generation with the generation of Sergei Korolyov, with those people who were behind modern-day space exploration," cosmonaut Musa Manarov said on popular Echo of Moscow radio.

"When I looked at him, I thought that everyone should live to be 100 because he continued having clarity of mind and memory and a great command of speech."

Chertok was also the author of numerous books.

He documented one of the world's most horrific but long-classified space catastrophes when dozens people were burned alive during a launch pad accident in 1960 at the Baikonur cosmodrome, known in the West as the Nedelin disaster.

The precise number of those perished when noxious rocket fuel exploded was hard to pin down but Russian space agency Roskosmos relies on figures provided by Chertok who put the number at 129.

After a wake Friday Chertok will be cremated and his ashes will then be laid to rest next to his wife, said Turchin.

Sending the first man into space in 1961 and launching the first Sputnik satellite four years earlier are among key accomplishments of the Soviet space programme and remain a major source of national pride in Russia.

The country has suffered some of its most embarrassing space mishaps in recent months, including the loss of a probe that aimed to bring back soil from Mars's largest moon Phobos.