GUNUNG SITOLI, Indonesia (AP) – Children returning to schools Monday for the first time since last week’s earthquake in Indonesia found classrooms destroyed and teachers missing.

Australia said its relief mission on the quake-hit Nias Island would continue despite the fatal crash of a navy helicopter on Saturday in which nine people were killed.

Survivors of December’s tsunami, meanwhile, marked 100 days since that disaster, remembering the dead with tears, prayers and readings from the Quran.

At the Santo Xaverius school, about 100 students sat on the basketball court looking at the remains of their three-story school, where the top floor had caved in.

“I heard that school will start today but I am disappointed because I have been told there will be no studies,” said Kurnia Faahakhododo, 19, a high school senior.

Thousands of other students in Nias’ main town, Gunung Sitoli, turned back in disappointment. Most school buildings were damaged and many teachers had not turned up.

At least 647 people, including 616 on Nias, have been confirmed killed in the 8.7-magnitude earthquake on March 28, national police spokesman Col. Zainuri Lubis said.

The region already was struggling with the aftermath of the Dec. 26 tsunami, which killed more than 126,000 people in Indonesia, mostly in Aceh province on nearby Sumatra island. Another 48,000 or more died in 10 other countries on the Indian Ocean rim.

In the fishing village of Kajhu in Aceh, hundreds gathered at a damaged mosque to mark the 100 days since the tsunami killed nearly 7,500 of its 9,400 residents.

According to Muslim tradition, the 100th day is observed by the reading of the “tahlil,” or prayer for the dead.

“This ceremony is very important for Muslim people. This is to calm the spirit of the dead and ensure that the spirit is accepted at Allah’s side,” said Herijal, a 25-year-old college student who lost his entire family in the tsunami.

Smaller prayer services were held across the province and the government will hold an official remembrance service Tuesday in the Aceh capital, Banda Aceh.

On Monday, the bodies of the Australian victims of Saturday’s helicopter crash were sent back home, said the head of the Australian relief mission, Cmdr. George McGuire.

“They gave their lives trying to help other people. The mission will continue. It is important we honor their memory,” McGuire told The Associated Press.

Meanwhile, a U.S. hospital ship, the USNS Mercy, was expected to arrive in the Nias vicinity late Monday and start treating patients on Tuesday, said Capt. Rick Morrison, the deputy surgeon for the U.S. Pacific fleet who is helping coordinate the ship’s medical mission.