JAKARTA, Dec. 27 (Xinhua) -- Flight authority in Indonesia has re-routed airway to avoid the risk of volcanic ash spewed from the Anak Krakatau volcano, as volcanologists have raised the level of danger, a senior official of transport ministry said Thursday.

The volcanologists have ratcheted up the alert level of the volcano amid fear of a second tsunami threat, which could be triggered by the eruption of the volcano. The eruption on Saturday night triggered tsunami and killed at least 430 people along the coast of Sunda Strait.

"The Air Nav has issued a notam ruling about the re-routing flight at the pathway which can not be passed by aircraft," said Polana B. Pramesti, director general of Air Transport of Indonesian Transport Ministry.

Rain of volcanic ash fell into the provincial capital of Banten and surrounding areas on Wednesday and local residents have been advised to use masks.

A satellite image shows that during the eruption on Dec. 22, most of the flank areas at the southwest of the volcano have collapsed just before the tsunami.

The country's meteorology and geophysics agency unveiled that the flank collapse covered an area of 64 hectares and caused landslides underwater.

Flight route, near the Sunda Strait where the volcano is situated, is one of the busiest pathways in Indonesia, with the country's largest international airport of Soekarno Hatta located in Banten province, where the volcano is situated.

Besides, the volcano is surrounded by several tourist resorts, the country's strategic industrial zone, a busy business shipping lane and some residential areas.

The volcanologist on Thursday raised the alert level of the volcano to the second highest from the third highest and widened no-go zone to 5 km from the crater from 2 km, spokesman of the national disaster management agency Sutopo Purwo NugrohoSutopo said.

The volcano has experienced "a strombolian" eruption since July, meaning that the volcanic activity produced frequent moderate eruption.

The tsunami has injured about 1,495 people and forced over 20,000 others to take shelters at evacuation centers for fear of the second tsunami threat, according to data from the disaster agency.

The catastrophe devastated a 312.75 km long of coastal areas, with most of the victims being retrieved in several tourist resorts in Pandeglang district of Banten province.

The Anak Krakatau volcano, or Child of Krakatoa volcano in English, is one of Indonesia's 129 active volcanoes in Indonesia, a vast archipelagic nation sits on a vulnerable quake-hit zone so called "the Pacific Ring of Fire."