When a blast jolted a Polish village near the Ukrainian border, resident Joanna Magus's first thought was that something had gone wrong at the nearby grain drying facility.

The reality was much more menacing -- a missile of controversial origin had struck Przewodow, killed two people and put the village at the centre of a dangerous episode in the Ukraine war.

"I'm scared. I didn't sleep all night," said Magus, 60, an elementary school teacher in the village that sits about six kilometres (4 miles) from the border.

"I hope it was a stray missile because otherwise we're helpless," she told AFP on her way to work in a place that is home to just a few hundred people.

Police investigators are seen during a searching patrol in the fields near the site where the missile strike killed two men in the eastern Poland village of Przewodow

Poland's President Andrzej Duda on Wednesday said it was "very likely" that the deadly missile was from Ukraine's air defence, and "absolutely nothing indicates that this was an intentional attack."

But the blast had immediately sparked concerns Tuesday that NATO might be drawn directly into Russia's war against Western-backed Ukraine, but the situation calmed as officials urged against quick judgement.

Poland's foreign ministry said the blast occurred at 1440 GMT on Tuesday, and residents said it hit a local grain drying facility, near a school.

When the missile struck, Magus was sitting at home, where her window looks out on the grain dryer.

"I heard a huge explosion, a terrible explosion, so I went up to the window and saw a huge cloud of dark smoke... I saw people running," she said.

"I thought maybe something had happened at the grain dryer, that one of the devices broke and exploded."

She said her husband was outside at the time, near the scene of the blast, so she called him and found out he "pretty much saw what happened."

"He was terrified, said something exploded and that two people were feared dead. It was total panic from there," she added.

'Didn't expect this'

The two victims were men around the age of 60, both involved with the local grain drying operation.

Ewa Byra, the principal of the elementary school, said that one of the dead was married to the school's cleaner. The other man was the father of a former student.

"We didn't really expect this sort of thing, even if accidents do happen, especially when the war is just six kilometres from the village," she told AFP.

Local authorities have declared three days of mourning following the blast.

An AFP journalist on the scene said the blast site was cordoned off, and a photo released by police showed a crater littered with metal debris and a lorry-sized vehicle flipped on its side.

The missile strike happened about six kilometers inside Poland's border with Ukraine.

Officers stood by the asphalt road leading into the village, which besides the school has just a smattering of buildings, a church and a cemetery.

Local parish priest Bogdan Wazny told AFP the area emptied out once news broke of the missile, and no one came to mass on Tuesday afternoon -- a first for the village.

He said he had been well-acquainted with both victims.

"They were very kind. They would lend a hand at the parish whenever I asked for help," Wazny told AFP.

"We redid the facade of the church recently and one of the men helped out."