REYKJAVIK, Iceland — Iceland warned airlines of a potential ash plume that may disrupt flights as one of the North Atlantic island’s biggest volcanoes erupted after a week of rumbling.

The aviation warning code was changed to “red,” signifying an “eruption is imminent or in progress — significant emission of ash into atmosphere likely,” the Icelandic Met Office said Saturday. Airspace above the eruption was closed, according to the island’s Civil Protection Agency.

The national police said scientists detected a “small subglacial eruption” in the northern part of Vatnajokull, Europe’s largest glacier. The Bardarbunga volcano, which lies beneath the glacier, is 15.5 miles wide and rises about 1,900 meters above sea level. It last erupted in 1996 and can spew ash and lava.

“The eruption is considered a minor event at this point,” the National Commissioner of the Icelandic Police said in the emailed statement. “Because of pressure from the glacier cap it’s uncertain whether the eruption will stay sub-glacial or not.”

No ash plume was visible, they said.

The seismic activity in Bardarbunga, which began Aug. 16, has raised concern that airlines may face a repeat of the 2010 disruptions when a cloud belched from the Eyjafjallajokull volcano forced carriers to cancel more than 100,000 flights and caused about $1.7 billion in lost revenue. Ash is a menace to jetliners because the glass-like particles can damage engines by melting and congealing.

“Right now, airlines are like an expectant father in a maternity ward’s waiting room.” said Henry Harteveldt, founder of Atmosphere Research Group, a travel-industry consulting firm in San Francisco. “However, instead of waiting for a bundle of joy, they’re waiting for an unwelcome volcanic eruption.”

Eurocontrol, the body that provides air-traffic control services across Europe, said Saturday a “danger area” had been declared around the volcano.

If ash were emitted, the Volcanic Ash Advisory Centre in London would release forecasts every six hours on its likely behavior and density, Eurocontrol said.

British Airways is “keeping the situation in Iceland under close observation” and “at present, all of our flights are operating normally,” it said in an emailed statement. A Virgin Atlantic flight was re-routed away from the volcano as a “precautionary measure,” spokeswoman Meigan Terry said in an email. All other Virgin Atlantic flights were operating normally, she said.

SAS, Scandinavia’s biggest airline, said it is monitoring the eruption and that it’s hard to tell how serious the situation will become, according to a statement.

American Airlines and United Continental each are monitoring the situation and haven’t changed their schedules, spokeswoman from the two U.S. carriers said.

The Icelandic police said they closed the Jokulsargljufur canyon and started to evacuate tourists there and around the Dettifoss waterfall.

“The situation at this stage doesn’t call for the evacuation of habitants in Kelduhverfi, Oxarfjordur and Nupasveit,” the police said. “People in those areas are encouraged to watch the news closely and have their mobiles switched on at all times.”