An aide of Robredo, Senior Inspector Jhun Abrasado, survived the crash but was injured. He returned to the crash site after being given first aid to assist with the search and rescue operations.
The plane, owned by Aviatour, was piloted by Jessup Bahinting, the company's chairman and CEO. He had a co-pilot, reportedly a Nepalese.
Transportation Secretary Manuel Roxas II described Bahinting as a "hero" in Cebu who flew despite stormy weather to deliver antivenom for a snake-bitten child.
President Benigno Aquino III is going to Masbate on Sunday, Lieutenant Colonel Julian Pacatan, commander of the 9th Infantry Battalion based in the province said.
There was some uncertainty over whether the search and rescue operations would continue into the night or be suspended.
Around 9 p.m., retired general Darius Tuason, head of the Provincial Disaster Risk Reduction and Management Council, said they had decided to suspend rescue operations and resume at 5 a.m. Sunday because the "waters are too deep and the area too dark."
Earlier, Tuason said the waters where the plane crashed are about 150 feet deep.
But News5's Ram Sison, who was onboard a rescue vessel, said the provincial government was continuing operations.
Roxas also said both surface and underwater operations were continuing.
"Site is 200 meters from shoreline. Surface search and rescue ongoing. Also diving search resumed using compressors," Roxas tweeted.
He also said an American Fleet Survey Team had joined the search for Robredo and the two pilos.
"Received and accepted offer of help via US Naval Attache Captain Jack Sutherland ... Fleet Survey team presently at site," Roxas tweeted.
Ronnie Nadal of the Masbate City government said parts of the plane have been recovered.
"Masyadong marami 'yung parts na nakuha sa dagat. Yupi-yupi talaga siya (There were so many parts recovered from the sea. They were really twisted)," he said.
News5's Sison also said the plane's tail has been recovered.
Helicopters from Manila and Lucena City are expected to arrive by Sunday to join police, military and Coast Guard rescue teams in the area, Bernardo Alejandro, director of the Office of Civil Defense in Bicol, said.
The Department of Interior and Local Government said the plane crashed into the sea off Masbate City as it attempted to make an emergency landing at the local airport. Bicol military spokesman Colonel Generoso Bolina told reporters the aircraft had encountered an unspecified engine problem.
Roxas described the plane as a Piper Seneca.
Philippine National Police spokesman Chief Superintendent Generoso Cerbo said the aircraft was only some 500 meters from the runway in Barangay Ibingay when it crashed at around 4:30 p.m.
Cauayan, Masbate Mayor Edgar Condor said they saw the airplane, already in trouble and flying erratically, pass his town, which is around 57 kilometers from the crash site.
"Nakita namin 'yung eroplano parang bumaba, parang helicopter na di na eroplano, parang abnormal na 'yung lipad niya, pababa ng pababa (We saw the plane descending and flying like it was a helicopter, no longer a plane, its flight path was abornal, it kept losing height)," he said.
Chief Superintendent Jose Arne delos Santos, Bicol police director, said the plane had come from Cebu and was headed for Naga City.
Interior Undersecretary Rico Puno, in an interview with radio station dzMM, said the plane was the same one Robredo had taken to Cebu.
Puno had joined Robredo in Cebu to attend the national summit of the Community Investigative Support and the Criminal Investigation and Detection Group, and saw the secretary off at the Cebu airport around 3 p.m.
Malacanang spokesman Edwin Lacierda, in a statement, called on the public "to join the President and the Cabinet in prayer for (Robredo's) successful rescue."
"We ask that the efforts be allowed to continue unimpeded and without speculation on the part of the public," he added. "We must remain focused on the task: to find Secretary Robredo and his companions, and to bring them to safey."
The Palace also announced a vigil for the successful rescue of Robredo at the National Shrine of the Divine Child inside the La Salle Greenhills campus in San Juan City.
"We ask those who wish to join our fellow citizens in prayer to go to LSGH and join their fellow citizens at this time of deep concern. We ask that you keep the family of Secretary Robredo and those engaged in rescue efforts in your prayers as well," the Palace said in a statement.