KARO, Indonesia (Reuters) - Indonesian officials warned on Monday against the prospect of further eruptions from an active volcano on the island of Sumatra after it emitted a huge column of ash, causing panic among residents.

Mount Sinabung, which has seen a spike in activity since 2010, erupted for around nine minutes on Sunday, sending clouds of volcanic ash 7 km (4.4 miles) into the sky.

Although no casualties were reported, officials monitoring the volcano warned of possible fresh eruptions.

“After the eruption, from midnight until 6 a.m., there were a few aftershocks,” said Willy, a scientist at a Sinabung observatory post, who uses one name, like many Indonesians.

Authorities left unchanged the alert level for Sinabung, but urged residents to use face masks and keep indoors to guard against volcanic ashfall.

Mount Sinabung, which is 2,460 m (8,071 ft) high, is among Indonesia’s most active volcanoes, but had been inactive for four centuries before its 2010 eruption. Indonesia has nearly 130 active volcanoes, more than any other country.