After a series of at times conflicting statements, the latest revelation underlined that authorities remain uncertain even where to look for the plane, and no closer to explaining what happened to Malaysia Airlines Flight MH370 or the 239 people on board.
Read: Hunt for missing Malaysian jet MH370 hits chaos, confusion
The flight disappeared from civilian radar screens shortly before 1:30 a.m. on Saturday, less than an hour after taking off from Kuala Lumpur, as it flew northeast across the mouth of the Gulf of Thailand bound for Beijing. What happened next is one of the most baffling mysteries in modern aviation history.
Timeline: The search for missing Malaysian jet
A woman stands in front of a placard featuring messages for passengers aboard a missing Malaysia Airlines plane at Kuala Lumpur International Airport in Sepang, Malaysia. (AP Photo)
Malaysian air force chief Rodzali Daud told a news conference that an aircraft was plotted on military radar at 2:15am, 200 miles (320 km) northwest of Penang Island off Malaysia's west coast.
It was not confirmed that the unidentified plane was Flight MH370, but Malaysia was sharing the data with international civilian and military authorities, Rodzali said.
"We are corroborating this," he added. "We are still working with the experts, it's an unidentified plot."
Full coverage: Missing Malaysian Airline flight MH370
India's coast guard joins search
India's coast guard joined the aerial search on Wednesday for the missing plane off the remote Andaman and Nicobar islands, a senior officer told AFP.
A Dornier aircraft belonging to the coastguard set off mid-afternoon local time to scour the eastern side of the Andaman islands on orders from the Indian government, the inspector general of the coastguard service said.
"We were directed to take part in the search operations up to the eastern fringes of the exclusive economic zone of the Andaman islands," VSR Murthy told AFP. "We are looking into that area for any clues to the missing airliner," he added.
The Andaman and Nicobar islands are Indian territory, although they are at least 1,000 kilometres (600 miles) from the mainland and are closer to the coast of Myanmar.
Indian Air Force on standby
Indian Air Force was on standby on Wednesday to search for the plane, as President Pranab Mukherjee said the country was ready to provide any help needed.
Indian Air Force spokesman Gerard Galway said planes were ready to deploy to scour the waters west of Malaysia for the passenger plane MH370.
"We have not received any task (as of now) but in case there is a requirement, our aircraft will be deployed to assist in the search operations," Galway told AFP.
Mukherjee said the country was ready to offer any assistance required and that officials were in constant contact with Malaysia over the plane's disappearance.
"We appreciate the efforts of the government of Malaysia to locate the missing aircraft and are ready to provide any help needed," Mukherjee's office said in a statement.
According to the data from Rodzali, if it was the missing plane it would have flown for 45 minutes and lost only about 5,000 feet (1,500 metres) in altitude.
There was no word on which direction it was headed and still no clue what happened aboard, prolonging the agonising wait for news for hundreds of relatives of those on board.
A position 200 miles northwest of Penang, in the northern part of the Strait of Malacca, would put the plane roughly south of the Thai holiday island of Phuket and east of the tip of Indonesia's Aceh province and India's Nicobar island chain.
Indonesia and Thailand have said their militaries detected no sign of any unusual aircraft in their airspace.
Read: Aliens? Suicidal pilot? Twitter turns into conspiracy potboiler over #MH370
The position is hundreds of miles west of the point where the Boeing 777-200ER dropped off air traffic control screens. Malaysia has asked India for help in tracing the aircraft and New Delhi's coastguard planes have joined the search.
Authorities however are continuing to search around both locations - at the last known position of the plane over the Gulf of Thailand and around the radar plotting site where the Malacca Strait meets the Andaman Sea.
In total, the search is over 27,000 square nautical miles (93,000 sq km), an area the size of Hungary or Indiana.
Until now, there has been no confirmed sighting of the plane or any debris.
A dozen countries are helping Malaysia in the search, with 42 ships and 39 aircraft involved, Transport Minister Hishammuddin Hussein said.
"My heart reaches out to the families of the passengers and crew," he said. "And I give you my assurance we will not reduce the tempo and that we will not spare any effort to find the missing plane."
A relative of a passenger on board missing Malaysia Airlines (MAS) flight MH370 cries as she arrives at the Everly hotel in Putrajaya. (AFP Photo)
Malaysia has been criticised for giving conflicting and confusing information on the last known location of aircraft.
Earlier on Wednesday, air force chief Daud had denied saying military radar had tracked MH370 flying over the Strait of Malacca.
Vietnam briefly scaled down search operations in waters off its southern coast, saying it was receiving scanty and confusing information from Malaysia over where the aircraft may have headed after it lost contact with air traffic control.
Pictures: Malaysian airliner mystery deepens
Hanoi later said the search - now in its fifth day - was back on in full force and was even extending on to land. China also said its air force would sweep areas in the sea, clarifying however that no searches over land were planned.
"As long as the plane is not found, we would continue doing our mission," Vo Van Tuan, spokesman for Vietnam Search and Rescue Committee, told reporters in Hanoi.
"We should always keep up hope, there can be miracles, human can survive for a long time in difficult conditions. We must not give up hope that the missing people are still alive."
Read: Conflicting information on plane's course 'pretty chaotic', says China
Nothing ruled out
In the absence of any concrete evidence to explain the plane's disappearance, authorities have not ruled out anything. Police have said they were investigating whether any passengers or crew on the plane had personal or psychological problems that might shed light on the mystery, along with the possibility of a hijacking, sabotage or mechanical failure.
The airline said it was taking seriously a report by a South African woman who said the co-pilot of the missing plane had invited her and a female companion to sit in the cockpit during a flight two years ago, in an apparent breach of security.
Deputy Commander of Vietnam 918 Air Brigade, Senior Lieutenant Nguyen Tri Thuc (R) looks for the missing Malaysia Airlines flight MH370, that disappeared from radar screens in the early hours of Saturday, off Con Dao island. (Reuters Photo)
"Malaysia Airlines has become aware of the allegations being made against First Officer Fariq Ab Hamid which we take very seriously. We are shocked by these allegations. We have not been able to confirm the validity of the pictures and videos of the alleged incident," the airline said in a statement.
The woman, Jonti Roos, told Reuters that she and her friend were invited to fly in the cockpit by Fariq and the pilot between Phuket, Thailand, and Kuala Lumpur in December 2011.
"I thought that they were highly skilled and highly competent and since they were doing it that it was allowed," Roos said. "I want to make it clear, at no point did I feel we were in danger or that they were acting irresponsibly."
Read: Malaysia seeks India's help in search for MH370
Hugh Dunleavy, the commercial director of Malaysia Airlines, told Reuters there was no reason to blame the crew.
"We have no reason to believe that there was anything, any actions, internally by the crew that caused the disappearance of this aircraft," he said.
The Boeing 777 has one of the best safety records of any commercial aircraft in service. Its only previous fatal crash came on July 6 last year when Asiana Airlines Flight 214 struck a seawall on landing in San Francisco, killing three people.
Read: 600,000 scan satellite images for clues to jet
US planemaker Boeing has declined to comment beyond a brief statement saying it was monitoring the situation.