A major eruption of Ecuador's Cotopaxi volcano is threatening up to 325,000 local residents, authorities in the South American country said on Monday.

Fast-moving mud and rock flow are of particular concern after Cotopaxi on Saturday shot ash more than two miles high and spilled some lava. Four hundred people were briefly evacuated over the weekend, the Associated Press reported.

Authorities had hoped to evaluate the situation with a flyover of the snow-capped, 19,600-foot volcano, but bad weather prevented the effort, top disaster official Maria del Pilar Cornejo said. Cotopaxi has shown activity since April, marking its first major eruption since 1877.

President Rafael Correa on Saturday declared a state of emergency, giving his government greater flexibility to mobilize financial resources to deal with the situation 30 miles south of the Ecuadorean capital of Quito, Reuters noted.

"We declare a state of emergency due to the unusual activity of Mount Cotopaxi," Correa said during his weekly Saturday address. "God willing, everything will go well and the volcano will not erupt."

Cotopaxi is considered one of the most dangerous volcanoes in the world, but Ecuador's Geophysical Institute said early Monday that no new ashfall and little sulfur smell had been detected in the area during the previous 24 hours, according to Phys.org.

The volcano's internal activity remained "high," though the surface activity was labeled "moderate," the website noted. The state of the volcano was "actively erupting," the Geophysical Institute summarized.

"No pyroclastic eruption have taken place, so there are no lava flows," security minister Cesar Navas explained, cautioning, however, that "there is evidence of fluid moving inside the volcano, as well as gas and magma."

Apparently to avoid panic, Correa decreed prior censorship Saturday on the volcano, meaning that local media are prohibited from publishing information about the eruption unless it comes from an official source, the AP noted. Press freedom groups, which have long been at odds with this administration's communications policies, criticized the president's move, the newswire added.

The Security Ministry of Ecuador continues to provide updates on social media, including its Twitter account, advising locals on essentials in case of continued eruptions.