REYKJANES PENINSULA, Iceland -- The major volcanic eruption in Iceland is prompting fears that dangerous toxic gas spewing into the air could reach the capital and put residents there at risk.
The new concerns from Iceland's meteorological office come as lava spews for miles across the Reykjanes Peninsula amid a state of emergency.
"They include a lot of very toxic materials, especially sulfur. So, locally, it can be really dangerous," said Dr. Christopher Hamilton, a volcanologist at the University of Arizona's lunar and planetary laboratory.
A guide took an ABC News crew near the rupture where the volcano is still spewing lava as high as 300 feet in the air.
"I guess for most of the people now, they know what's going on. We were just waiting -- where will it start? Where will the fire come up," said Pall Halldorsson, a rescue volunteer.
Officials are warning tourists to stay away but some are catching glimpes of it on their travels.
"For the moment, we're grounded," said Andrew Jones, who is returning from a 50th birthday trip. "We are waiting here on the runway."
Since the eruption, Iceland's meteorological office measured more than 300 earthquakes. Experts say the intensity has weakened but three of five vents are still erupting.
It's unclear how long the eruption will last. Officials say the size in the ground is bigger than expected and the speed the lava is moving is faster than anticipated. While the nearby town and power plant remain unaffected, they are still not in the clear.