Boeing 737: Singapore bars entry and exit of 737 Max planes
Singapore's Civil Aviation Authority has temporarily suspended the Boeing 737 Max fleet of aircraft from flying into and out of the country.
The decision comes after an Ethiopian Airlines Boeing Max 8 crashed on Sunday, killing 157 people on board.
It was the second fatal accident involving that model in less than five months.
Singapore's Changi Airport is the world's sixth busiest and a major hub connecting Asia to Europe and the US.
But only a handful of airlines operate Max aircraft in and out of the country.
Several airlines and regulators around the world have already grounded the Max 8 model following the crash.
Singapore is believed to be the first country to ban all variants of the Max fleet of aircraft. The suspension went into effect from 14:00 local time (06:00 GMT).
Is disruption likely?
Singapore's aviation authority said the affected airlines include SilkAir, which operates six Boeing 737 Max 8 aircraft, as well as China Southern Airlines, Garuda Indonesia, Shandong Airlines and Thai Lion Air.
It said it is working with airlines and Changi Airport to minimise the impact on passengers. Experts told the BBC that disruption was likely, however.
Aviation consultant Ian Thomas said: "This is sure to lead to significant flight cancellations and disruption to schedules as the airlines involved switch to other aircraft types (assuming they are available)."
The BBC's Karishma Vaswani, who is at Changi Airport, reports orderly scenes. Some flights have been cancelled but it is not known if the suspension is to blame.
In the US, the country's Federal Aviation Administration (FAA) told airlines on Monday it believes Boeing's 737 Max 8 model to be airworthy, despite the two fatal crashes.
What is a Boeing 737 Max aircraft?
The Boeing 737 Max fleet of aircraft are the latest in the company's successful 737 line. The group includes the Max 7, 8, 9 and 10 models.
By the end of January, Boeing had delivered 350 of the Max 8 model out of 5,011 orders. A small number of Max 9s are also operating.
The Max 7 and 10 models, not yet delivered, are due for roll-out in the next few years.
The Max 8 that crashed on Sunday was one of 30 ordered as part of Ethiopian Airlines' expansion. It underwent a "rigorous first check maintenance" on 4 February, the airline said.
Following last October's Lion Air crash in Indonesia, investigators said the pilots had appeared to struggle with an automated system designed to keep the plane from stalling, a new feature of the jet.
It is not yet clear whether the anti-stall system was the cause of Sunday's crash. Aviation experts say other technical issues or human error cannot be discounted.
What have US authorities said?
US aviation officials have said the 737 Max 8 is airworthy and that it is too early to reach any conclusions or take any action.
US Transportation Secretary Elaine Chao on Monday said the FAA would "take immediate and appropriate action" if a defect was found in the Max 8.
Boeing has confirmed that for the past few months it has been developing a "flight control software enhancement" for the aircraft.
Paul Hudson, the president of FlyersRights.org and a member of the FAA Aviation Rulemaking Advisory Committee, nonetheless called for the plane to be grounded.
"The FAA's 'wait and see' attitude risks lives as well as the safety reputation of the US aviation industry," Mr Hudson said in a statement on Monday.