A search and rescue (SAR) helicopter crashed into sea in Indonesia's Marina Beach of Semarang, the provincial capital of Central Java, detikcom online news reported on Wednesday.

The accident occurred at 0930 local time (0230 GMT) and three of the five crew members aboard were injured.

"All injured crew members have been brought to a hospital," said a SAR official who declined to be identified.

According to the provincial police chief inspector General Alex Bambang Riatmodjo, the cause of the accident is that the helicopter flew too low.

"Information to me said that the helicopter flew so low that its bottom touched the sea surface and crashed," said Alex at the accident scene.

Alex admitted that he was not sure whether the helicopter's engine was damaged. However, according to the information from the national SAR Agency, the helicopter was proper to fly.

According to Alex, police will help the evacuation process. But, it should wait for equipment from Jakarta.

The helicopter crashed while it was in a rescue training joined by 44 SAR officials.

An eyewitness said that he heard a loud explosion when the helicopter crashed.

"Once the bottom approached the water surface, the helicopter was unsteady and bumped (the water surface). I heard a loud noise of explosion," Lukito, the eyewitness, told detikcom.

One of the SAR officials confirmed the explosion.

"The noise was so loud that it could be heard from the beach," he said.