"Unfortunately, we have not found anything that appears to be objects from the aircraft, let alone the aircraft itself," Azharuddin Abdul Rahman, head of Malaysia's Department of Civil Aviation, said at a news conference.
"This unprecedented missing aircraft mystery -- it is mystifying and we are increasing our efforts to do what we have to do," he said.
The Beijing-bound Boeing 777-200 Flight MH370 of Malaysia Airlines had 227 passengers aboard, including five Indians and one Indian-origin Canadian, and 12 crew members.
Rahman said investigators were pursuing "every angle" to explain its disappearance, including hijacking.
Malaysia yesterday launched a terror probe into the disappearance of the plane that suddenly vanished from the radar one hour after taking off from Kuala Lumpur Airport on Friday midnight.
The probe was launched after it emerged that two passengers boarded the flight with stolen passports of an Italian and Austrian. Preliminary investigation also indicated that plane may have turned back.
One of the two suspects, who travelled on the plane on stolen passports has been identified.
"I can confirm that he is not a Malaysian, but cannot divulge which country he is from yet," Inspector General of Police Khalid Abu Bakar said in Kuala Lumpur. He said both suspects had no record of entering the country legally.
Five passengers holding tickets had failed to board that flight, Rahman said.
"Their luggage was off loaded and would not have been in the plane. All check in luggage was screened," he said.
Vietnam today scrambled aircraft to check up if a lifeboat-like floating object found in Vietnamese waters was from the missing plane, official Chinese media reported.
Malaysia informed Vietnam that it spotted the lifeboat- like object in sea and asked Vietnam to verify if it belongs to the missing plane.
Vietnamese searchers on ships worked throughout the night but could not find a rectangle object spotted yesterday that was thought to be one of the doors of the plane.
Rahman said Vietnamese officials had not confirmed to Malaysia, reports that debris believed to be from the plane had been found.
The Malaysian official said the authorities were as "puzzled" as others over the disappearance of the plane.
Home Minister Ahmad Zahid Hamidi yesterday said the two passengers who used stolen passports to board the plane had "Asian facial features"
"I am still puzzled how come (immigration officers) cannot think, an Italian and Austrian (passengers) but with Asian facial features," he told reporters yesterday.
Asked about how the two passengers with Asian features could have been allowed to pass, Rahman said the investigating officials were looking into it.
He stressed that search efforts had been intensified expanding area of search to the Andaman sea.
"There are a number of reports, number of sightings that we have made. The Malaysian Maritime Enforcement agency also spotted slicks in the South China Sea and they took samples of it and those samples have been sent to the labs," Rahman said.
The list of passengers on board the plane included 154 Chinese, 38 Malaysians, 7 Indonesians, 6 Australians, 5 Indians, 4 Americans and 2 Canadians.
Indians have been identified as Chetna Kolekar, 55, Swanand Kolekar, 23, Vinod Kolekar, 59, Chandrika Sharma, 51, and Kranti Shirsatha, 44.
Rahman said, "There are various objects our team has seen but none of them confirm any of them are from the aircraft. And for the aircraft to just go missing just like that from the radar...We are equally puzzled. The honourable Prime Minister used the word 'perplexing'."
"To confirm what had happened on that particular day to the ill-fated aircraft, we need hard evidence, we need concrete evidence.
"Every hour, minute, second we are looking for the plane. We are looking at every inch of sea," he said.
Officials from the US Federal Aviation Administration and the US National Safety Transportation Board have arrived to help in the investigation.
The plane has not emitted any signal from the time it went missing. A massive search operation was launched after the disappearance of the aircraft with 40 vessels and 24 planes scouring the Malaysian, Vietnamese waters and the Andanan Seas in a multi-nation operation.
Meanwhile, almost 20,000 fishermen were set to join in search operations.
Malaysia's Agriculture minister Ismail Sabri Yaakob said 1,800 Malaysian fishing vessels in the South China Sea and Straits of Malacca had been told to assist in the search and rescue efforts.
Meanwhile, Thai Navy Commander-in-Chief Adm Narong Pipattanasai has dispatched a patrol vessel from Phang Nga in the Andaman Sea to help search for the missing plane.
The vessel joined the search near the Strait of Malacca. The operation was backed up with a helicopter and a patrol plane.
Navy secretary Rear Adm Kan Deeubol said the Thai Navy helped search near the Andaman side as the other side of the strait has already been searched by Vietnamese and Singapore navies.