There has been a rush to buy medical iodine in Russia's far north, following a brief radiation spike linked to a rocket accident, Russian media report.
Pharmacies' stocks of iodine are reported to be running out in the cities of Arkhangelsk and Severodvinsk.
Iodine can block the thyroid gland's take-up of radioactive iodine, but the pills can also cause medical problems.
Two people died and six were injured in Thursday's accident at a test site. But the military has given few details.
The Severodvinsk administration said radiation levels were higher than normal for about 40 minutes, but then returned to normal. The city of nearly 200,000 is about 47km (29 miles) east of Nyonoksa, where the explosion took place.
The Nyonoksa site carries out tests for virtually every missile system used by the Russian navy, including sea-launched intercontinental ballistic missiles, cruise missiles and anti-aircraft missiles.
The defence ministry said a liquid-fuel rocket engine had exploded, but it did not specify the system involved.
The navy is now keeping all shipping out of nearby Dvina Bay, on the White Sea, for a month. But an Arkhangelsk port official told the BBC that it was a planned closure, which had been announced before the Nyonoksa blast.
Severodvinsk has a shipyard that builds and repairs nuclear submarines for Russia's Northern Fleet.
Pharmacists in Arkhangelsk told Russia's Interfax news agency on Friday that stocks of iodine were running out, such was the demand.
"Yesterday it was all sold out," said one pharmacist, noting that all forms of iodine in her shop had been snapped up by shoppers.
"The excitement started at about five o'clock, and they bought all of it before we closed. At the checkout people were discussing the news about radiation in Severodvinsk, the explosion at the military site."
Another pharmacist had a similar story and said she had put in an urgent order for more iodine.
The rush for iodine was also reported earlier by a news website for the Arkhangelsk region, 29.ru.
Low-level radiation spike
It also said medics who evacuated the injured at Nyonoksa wore chemical and nuclear protection suits.
There was a rush on iodine stocks during the 1986 Chernobyl nuclear disaster in Ukraine, which sent a huge plume of radiation across Europe.
On Thursday the Severodvinsk administration reported a 40-minute spike in radiation, which reached 2 microsieverts per hour, then fell back to the normal 0.11 microsieverts. Both levels are too small to cause radiation sickness.
The administration has now deleted its statement online about the spike. The BBC asked officials there why, and they said "because this incident comes under the authority of the defence ministry".
The defence ministry insisted that "there have been no harmful chemicals released into the atmosphere, the radiation levels are normal".
Arms dump explosions
On Friday shells started exploding again at a military dump in the Krasnoyarsk region of Siberia, thousands of miles east of Arkhangelsk.
At least nine people were injured, and residents of the nearby village of Kamenka were evacuated again. A lightning strike is reported to have triggered the latest explosions.
The army had earlier extinguished a huge fire at the depot, which set off massive explosions for hours on Monday.
One person was killed and eight others were injured in that blaze.