CHICAGO (CBS/CNN) — The United Kingdom and at least six other nations have halted flights of Boeing 737 Max 8 planes in their airspace, following two deadly crashes involving the aircraft in the past six months.

On Sunday, Ethiopian Airlines flight 302 crashed near Addis Ababa, Ethiopia, killing all 157 people on board. In October, a Lion Air flight crashed into the Java Sea off Indonesia, killing all 189 passengers and crew.

Both crashes involved Max 8 aircraft, which nosedived shortly after takeoff.

“Given the similarity of the two accidents, it has been decided that as a precautionary measure that all Boeing 737-8 ‘MAX’ and Boeing 737-9 ‘MAX’ operations in the United Kingdom, whether by UK AOC holders or foreign AOC holders and carriers, should stop until appropriate safeguards are in place,” UK Civil Aviation Authority officials said in a statement Tuesday.

British officials said there are five Max 8 planes registered and operating in the United Kingdom, with a sixth that had been set to begin operations later this week.

Authorities in Germany, China, Singapore, Australia, Malaysia, and Oman also have temporarily suspended flights of the Max 8, or otherwise closed their airspace to the planes.

The FAA is not grounding the 737 Max 8, but is ordering Chicago-based Boeing to begin safety-related software enhancements on those planes by next month.

There are 74 of these planes used in the United States and 387 worldwide.

The changes to the Boeing jets have been in the works since the Lion Air crash in October.

One of the changes includes updates to the anti-stall system, which automatically points the plane’s nose down if sensors find the plane could be in danger of losing lift.

In a statement, Singapore’s Civil Aviation Authority announced it would suspend all variants of the Boeing 737 Max aircraft from entering or leaving the city-state, a move affecting SilkAir, China Southern Airlines, Garuda Indonesia, Shandong Airlines and Thai Lion Air.

While no Australian airlines fly the 737 MAX, Australia’s Civil Aviation Safety Authority said it would temporarily suspend airlines from flying all Boeing 737 MAX jets to or from Australia.

Oman said on Twitter it is temporarily suspending operations of Boeing 737 MAX aircraft into and out of its airports until further notice.

Malaysia announced that it would suspend the Max 8 aircraft flying to or from and transiting the country until further notice. No Malaysian carriers currently operate the model.

Airlines including Ethiopian Airlines, Aeromexico, Cayman Airways, South Africa’s Comair, South Korea’s Eastar Jet and Aerolíneas Argentinas and all Indonesian airlines have said they are temporarily not using the 737 Max 8.

Those decisions follow the lead of China’s aviation administration, who on Monday ordered that all domestic Boeing 737 Max 8 jets be out of the air by 6 p.m. local time, due to its principle of “zero tolerance for safety hazards.”

China has one of the world’s largest fleets of Boeing 737 Max 8, operating 97 of the planes, according to Chinese state-run media.

The fallout has appeared to affect Boeing’s bottom line. The aircraft maker’s stock dropped 8% Monday, with investors voicing concerns about the 737 and Boeing’s future in China, predicted to soon become the world’s first trillion-dollar market for jets.

Growing concern

While there is no evidence of a link between the incidents in Ethiopia and Indonesia, similarities between the two have prompted some airlines to take extra safety precautions while both crash investigations are ongoing.

“Given in both air crashes, the aircrafts were newly delivered Boeing 737 Max 8, and both accidents occurred during the take-off, they share certain similarities,” the Chinese aviation administration said in a statement Monday. It added that it would contact Boeing and the U.S. Federal Aviation Administration (FAA) to confirm “flight safety” issues before allowing the planes to fly again.

While some international airlines and governments grounded the 737 Max 8 planes, US airlines, the FAA and Boeing had not.

CNN aviation expert Richard Quest said of the CAA’s decision, “the pressure is now intensifying on the FAA (the US Federal Aviation Administration) when world-respected authorities like the CAA and Australian Civil Aviation Safety Authority have safety concerns about the aircraft.”

“It will be very difficult for the FAA to withstand the pressure to actually do something rather than just adopting this wait-and-see approach.”

And aviation safety experts and regulators around the world remain divided on whether the Boeing 737 Max 8 is safe to fly.

“I’ve never said that it’s unsafe to fly a particular model of aircraft, but in this case, I’m going to have to go there,” David Soucie, a former FAA safety inspector told CNN, saying that passengers don’t have enough information.

Peter Goelz, a former managing director of the National Transportation Safety Board (NTSB) said he believes it’s too early for American authorities to ground the jets.

On Monday, Charlie Miller, vice president of communications for Boeing, issued a statement saying the jetliner manufacturer is not planning to issue new guidance “at this point” noting that “the investigation is in its early stages.”

(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. The CNN Wire contributed to this report.)