Secrecy surrounding an explosion that killed five nuclear scientists and caused a spike in radiation levels has sparked fears of a cover-up in Russia, with authorities backflipping on orders to evacuate a nearby village.

Key points: Medics who treated victims of an accident have been sent to Moscow for medical examination

Medics who treated victims of an accident have been sent to Moscow for medical examination Russia's state weather service said radiation levels spiked in Severodvinsk by up to 16 times

Russia's state weather service said radiation levels spiked in Severodvinsk by up to 16 times Many Russians spoke angrily on social media of misleading reports reminiscent of Chernobyl

The explosion took place on Thursday at a naval weapons range on the coast of the White Sea in northern Russia.

State nuclear agency Rosatom said the accident occurred during a rocket test on a sea platform.

The rocket's fuel caught fire after the test, causing it to detonate, it said in a statement carried by Russian news agencies.

Two days later, after a spike in radiation levels was reported, Rosatom conceded the accident involved nuclear materials.

On Tuesday (local time), the Russian military ordered residents of the small village of Nyonoksa to temporarily evacuate, citing unspecified activities at the nearby navy testing range.

But a few hours later, it said the planned activities were cancelled and told the villagers they could go back to their homes, said Ksenia Yudina, a spokeswoman for the Severodvinsk regional administration.

Local media in Severodvinsk said Nyonoksa residents regularly received similar temporary evacuation orders, usually timed to tests at the range.

Russia's state weather service said radiation levels spiked in the Russian city of Severodvinsk, about 30 kilometres west of Nyonoksa, by up to 16 times following the explosion.

Emergency officials issued a warning to all workers to stay indoors and close the windows, while spooked residents rushed to buy iodide, which can help limit the damage from exposure to radiation.

'People need reliable information'

The five scientists that died in the explosion were buried Monday in the closed city of Sarov. ( AP: Russian State Atomic Energy Corporation ROSATOM )

Many Russians spoke angrily on social media of misleading reports reminiscent of the lethal delays in acknowledging the Chernobyl accident three decades ago.

US experts said they suspected the cause was a botched test of a nuclear-powered cruise missile commissioned by President Vladimir Putin.

Boris L Vishnevsky, a member of the St. Petersburg City Council, told the New York Times that dozens of people had called asking for clarification about radiation risks.

"People need reliable information," Mr Vishnevsky told the Times.

"And if the authorities think there is no danger, and nothing needs to be done, let them announce this formally so people don't worry."

The five scientists that died in the explosion were buried Monday in the closed city of Sarov — which houses a nuclear research facility and is surrounded by fences patrolled by the military.

While hailing the deceased as the "pride of the atomic sector", Rosatom head Alexei Likhachev pledged to continue developing new weapons.

"The best tribute to them will be our continued work on new models of weapons, which will definitely be carried out to the end," Mr Likhachev was quoted as saying by RIA news agency.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 36 seconds 36 s Russia has been testing a new generation of nuclear-capable weaponry

Medics who treated victims sent to Moscow

Medics who treated the victims of an accident were sent to Moscow for medical examination, TASS news agency cited an unnamed medical source as saying on Tuesday.

The medics sent to Moscow have signed an agreement promising not to divulge information about the incident, TASS cited the source as saying.

US President Donald Trump said on Twitter on Monday the United States was "learning much" from the explosion and the United States had "similar, though more advanced, technology".

He said Russians were worried about the air quality around the facility and far beyond, a situation he described as "Not good!"

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But when asked about his comments on Tuesday, the Kremlin said it, not the United States, was out in front when it came to developing new nuclear weapons.

"Our president has repeatedly said that Russian engineering in this sector significantly outstrips the level that other countries have managed to reach for the moment, and it is fairly unique," Kremlin spokesman Dmitry Peskov said.

Mr Putin used his state-of-the nation speech in 2018 to unveil what he described as a raft of invincible new nuclear weapons, including a nuclear-powered cruise missile, an underwater nuclear-powered drone, and a laser weapon.

Tensions between Moscow and Washington over arms control have been exacerbated by the demise this month of a landmark nuclear treaty.

ABC/wires