Authorities in Iceland are warning people to stay away from a volcano that spectacularly erupted Monday and forced the evacuation of thousands of people — but hordes of gawkers are still flocking to the dangerous site.

The Reykjanes volcano spewed fiery lava and clouds of thick black smoke Monday night into Tuesday morning — as stunned airplane passengers took off and landed in the island nation.

A flight bound for Suomi in Finland flew directly over the volcano in the southwest part of the country, giving passengers a bird’s-eye view of its rivers of orange magma flowing against the dark morning sky Tuesday.

British tourists temporarily stranded on the runway of Reykjavik’s international Keflavik airport posted footage of themselves shouting, “Oh my God!” as they watched the magma and flames turn the sky red.

The Icelandic government has insisted the volcanic eruption at Sundhnuksgígar does not currently “present a threat to life” — although authorities evacuated nearly 4,000 inhabitants of the nearby fishing town of Grindavik last month as the volcano began exhibiting signs of an impending explosion.

Authorities added that “international flight corridors remain open.”

But the government — which makes about $3.5 billion a year from tourism, according to Statista — is still urging people to keep their distance.

“People are strongly warned not to approach the area for their own safety and in order not to disrupt the traffic and the work of responders,” officials said in a statement, according to Yahoo News.

“We ask people to allow us to assess this situation, this is not a tourist attraction,” said Hjálmar Hallgrímsson, a police field commander.

“This is many times more powerful,” he said, the Telegraph reported.

But gawkers and thrill-seekers have been flocking to the area.

After Monday night’s eruption, people were seen in a line of cars trying to get closer, according to The Mirror.

“It’s just something from a movie!” said Robert Donald Forrester III, a tourist from the United States.

Icelandic residents told local media they always travel to see the eruptions in Reykjanes.

“We are trying to see the eruption. Unfortunately, we didn’t get any closer,” a resident said, according to The Mirror. “It’s a hobby that we’ve had for four years, attending every single eruption, and we’ll continue to do so.”

The volcano had been emitting 100 to 200 cubic meters of lava every second at first, which the Norwegian Meteorological Agency said is “many times more than in previous eruptions on the Reykjanes Peninsula in recent years.”

By early Tuesday afternoon, the Icelandic Meteorological Office reported that the size of the volcanic eruption “continues to diminish.’’ It said the lava flow was estimated to be a quarter of what it was at the time of the eruption. 

The eruption’s lava ”fountains,’’ which have reached as high as 30 yards, have also been falling.

With Post wires