SEMARANG, Indonesia (AP) — An Indonesian army helicopter crashed on the main island of Java on Saturday, killing four of the nine people on board, officials said.

The Russian-made MI17 helicopter was carrying nine soldiers on a training mission when it went down and burst into flames in Central Java province’s Kendal district about an hour after taking off from the provincial capital, Semarang, said army spokesman Brig. Gen. Nefra Firdaus.

In addition to the four who were killed, five others were hospitalized with serious injuries after managing to escape the wreckage, Firdaus said in a statement.

The cause of the crash was not immediately known.

“The helicopter was flying very low and getting lower until it crashed with a very loud sound,” Eka, a witness, was quoted as saying by Kompas TV. “Two passengers escaped before it crashed, and after that there were three or four explosions.”

Indonesia, a sprawling archipelago nation of about 270 million people, has been plagued by transportation accidents in recent years, including plane crashes and ferry sinkings.

The military, which suffers from low funding, has also regularly suffered airplane and helicopter crashes.