Indonesia's disaster agency says 30 people were treated for gas exposure after Mount Ijen in eastern Java belched toxic fumes from its crater.

Spokesman Sutopo Purwo Nugroho said Thursday that dozens of residents of several villages on the volcano's slopes had to flee.

The mountain has a stunning sulfur lake but at night, low-paid laborers engage in the dangerous back-breaking work of mining sulfur.

Sutopo said Ijen's summit is now temporarily off limits to activities but the volcano's overall status remains normal.