Soon after the plane carrying 239 people vanished on March 8, authorities revealed that two passengers had boarded it using stolen passports in a major breach of airport security that triggered fears of a terror link.

Malaysia believes the flight was deliberately diverted by someone on board. But the absence of firm evidence of the plane's fate has fuelled intense speculation and a wealth of conspiracy theories, including a hijacking.

Changi is an "international gateway" where nearly 7,000 flights land or depart weekly and 147,000 passengers pass through daily, the Singapore police said in a statement.

"Arising from the MH370 incident, the Singapore Police Force (SPF) and Immigration & Checkpoints Authority (ICA) have raised the security alert at Changi Airport as a precautionary measure," the statement said.

The statement did not give details of the additional steps taken.

Security measures at the airport are "in accordance with international best practices and the security standards prescribed by the International Civil Aviation Organisation (ICAO)," it said.

"The Police and ICA are monitoring the security threat situation closely," the statement said.

"We appreciate the understanding and patience from travellers as we conduct the various security checks to ensure safe and secure travel."

Flight MH370 disappeared from civilian radar 16 days ago, nearly an hour after taking off from Kuala Lumpur for Beijing.

Chinese passengers comprised two-thirds of the 239 people aboard the Boeing 777 aicraft.

A massive international search is currently under way in the southern Indian Ocean after satellite data indicated the plane may have ended up there, with evidence mounting of debris in the area that may be connected to the mystery.