The Philippine Institute of Volcanology and Seismology said it raised the alert level for Taal Volcano because a growing number of volcanic earthquakes and a sharp rise in carbon dioxide emissions indicated rising magma.

It said 21 quakes were recorded over a 24-hour period ending early Saturday.

The institute warned that sudden explosions and high concentrations of toxic gas could be lethal to people and animals.

Taal, a tourist destination about 45 miles (75 kilometers) south of Manila, was declared off-limits to visitors as of Saturday, said Senior Inspector Manuel Maligaya, police chief of Talisay township on the shores of the lake in Batangas province.

Local officials also warned lakeside resort owners not to allow their guests to visit the island volcano.

The volcano has erupted more than 30 times since the 16th century. An eruption in 1911 killed nearly 2,000 people. A mild eruption in 1977 caused no damage or injuries. [ MSNBC ]