A video posted on Kompas TV showed the explosions sending plumes of black smoke high into the sky. 

According to residents, three big explosions were heard from 7 a.m. on Saturday after dozens of small explosions that lasted around an hour. Brimob personnel were immediately moved residents near the location after the initial explosion.

The injured officer, Adj. Sr. Comr. Syaiful Anwar, was the bomb squad unit head, who suffered wounds to his left hand and head.  

Central Java Police chief Insp. Gen. Rycko A Dahniel said the facility caught fire before the explosion. It is not yet clear where the fire started, but the explosions came from the grenades and other explosives stored in the warehouse. 

He said the police would study the cause of the explosions through CCTV footage at the location.

The warehouse is located around 100 meters from the residential area and the closest building was the injured policeman’s home. The location is also in the separated area from the Brimob’s ammunition warehouse and its dormitory, and therefore met the standard operational procedure, according to Rycko.

“It’s located at a warehousing and truck parking area,” Rycko said on Saturday.

National Police spokesman Brig. Gen. Dedi Prasetyo said there were 33 high explosive remnants of World War II stored at the warehouse, consisting of various types of mortars measuring around 30 to 120 centimeters with a diameter of around 25 to 80 cm and grenades.

Dedi suspected that the blast was triggered by high air temperatures as the decades-old bombs had become brittle with age and sensitive to vibrations and shock, including temperature. The police's bomb squad (Gegana) are currently checking the location to make sure of the cause.

"When the temperature rises it triggers an explosion. The oldest [bomb] may explode first and triggered the others,” Dedi said.

The Central Java Police will soon repair the damaged houses and the policeman who suffered minor injuries to his hands and head due to the blast debris had received quick treatment at Banyumanik Hospital.

Kasmirja, 62, a food vendor near the location said he heard around three to five times loud explosions followed by many small explosions sounding like fireworks. An access road to Surakarta and Yogyakarta had been closed temporarily.

“But the police responded quickly,” he said.

A resident near the area, Purwanti, 25, said she was riding a motorcycle when the incident happened.

“As soon as I heard an explosion, I stopped and residents rushed out of their houses to see the cause," she said. (ggq)