Navy spokesman Col. Omar Tonsay said three Navy ships had been sent to the area, but rescuers were having difficulties finding Robrero and the two missing pilots -- Jessup Bahinting and Kshitiz Chand -- because of poor visibility, depth of the waters, a strong current and the extent of the crash site.
Robredo's security aide, Senior Inspector Jun Abrazado, was rescued shortly after the Piper Seneca aircraft crashed into the waters Saturday.
The United States had also sent a rescue team to Masbate Bay, the Manila Bulletin reported.
Philippines President Benigno S. Aquino III flew to Masbate Sunday to oversee the search and rescue operations. Robredo and Aquino are close friends, the newspaper reported.
"Throughout the night, search and rescue operations for Secretary Jesse Robredo and party continued. More assets are being deployed this morning to intensify the search," presidential spokesman Edwin Lacierda said.