The reports came after Russia launched a wave of attacks across Ukraine, but it is not yet clear what has happened, the BBC said.

Ukraine was hit by over 90 missiles on Tuesday, according to Ukraine's Air Force spokesperson Yuri Ihnatw, who said more than 70 were successfully shot down.

The Polish government has also not commented, but said it was putting some military units on heightened alert after holding an emergency meeting.

Earlier, some Polish media said Russian missiles had crossed the border from Ukraine and fallen on Poland.

Ukraine and Russia have traded blame, with Ukrainian President Volodymyr Zelensky accusing Moscow of deliberately attacking Poland.

Russia dismissed claims it was responsible, calling them "a deliberate provocation in order to escalate the situation".

The US and other international powers said they were investigating but are yet to apportion blame.

Polish firefighters have confirmed two people were killed in the explosion in the eastern town of Przewodów, without giving the cause of the blast.

An image being shared online shows what appears to be a large crater on what local media reports is Polish farmland, suggesting missile damage. Another image appears to show a fragment of a missile.

If the missiles were confirmed to be Russian, it would mark the first time its missiles had landed on a Nato member, raising the question of how the security alliance might respond.

President Zelensky said it was a "significant escalation" in Moscow's war - and warned it was "only a matter of time before Russian terror goes further".

Russian state news agency Ria Novosti said it was instead Ukrainian missiles that had hit Polish territory.

Neither of these allegations have been substantiated.

Nato Secretary General Jens Stoltenberg said he has spoken to Polish President Andrzej Duda and the military alliance was "monitoring the situation", the BBC report added.

"Allies are closely consulting," he said on Twitter. "Important that all facts are established."

(With UNI inputs)