It means that the authorities, like the police, etc, are afraid that hundreds of people could be dead. "He feared that hundreds (of people) were dead." means the same as "He was afraid that hundreds (of people) were dead."

It is thought that hundreds of people died, but it remains unconfirmed. It suggests that perhaps less died but one fears that hundreds died.

Jmat ，thank you！

oh，I see

'To be' is often omitted in newspaper titles to save space. The full sentence is "Hundreds are feared to be dead".