Iceland's authorities on Sunday raised the aviation warning code to red for a region close to the subglacial Bardarbunga volcano after a small fissure eruption in the area.

The country's meteorological agency described the eruption in the Holuhraun lava field, about five kilometers (three miles) north of the Dyngjujoekull glacier, as a "very calm lava eruption and can hardly be seen on seismometers."

Icelandic aviation authorities closed the airspace around the eruption area up to 6,000 feet. Most commercial flights won't be affected because they fly much higher than that.

No volcanic ash has been detected, and the Civil Protection Department said all Icelandic airports remained open.

Sunday morning's eruption, which took place about 0500 GMT (1 a.m. EDT), was the third one in the area since Aug. 23. On Friday, a smaller fissure eruption in the same site also prompted authorities to briefly raise the aviation warning code to restrict flights around the eruption site.

Authorities said Sunday's eruptive fissure was longer than the previous one, and was extending north and south.

"Visual observation confirms it is calm, but continuous," the weather agency said on its website.

The Bardarbunga volcano lies under the Vatnajokull glacier, which dominates the eastern corner of Iceland. Though remote and sparsely populated, the area is popular with hikers in the summer. Officials earlier evacuated all tourists in the region in response to intense seismic activity there.

In 2010, an eruption at the Eyjafjallajokul volcano caused a week of aviation chaos and wreaked havoc on millions of travelers. More than 100,000 flights were canceled after officials closed Europe's air space for five days out of fear that volcanic ash could damage jet engines.