Updated

Frightened residents fled a bustling city of 400,000 at the foot of Indonesia's rumbling volcano Monday, cramming onto trains, buses and rented vehicles as authorities warned Mount Merapi could erupt again at any time.

A mass burial late Sunday for many of the 141 people killed in the last two weeks served as a reminder of the mountain's devastating power that culminated in its deadliest blast in 80 years that sent hot clouds of gas, rocks and debris avalanching down its slopes.

"My parents have been calling ... saying 'You have to get out of there! You have to come home!"' said Linda Ervana, a 21-year-old history student who was waiting with friends at a train station in the university town of Yogyakarta, 20 miles (30 kilometers) away.

After failing to get tickets, they rented a minibus with other classmates.

"It feels like that movie '2012,"' said her 22-year-old friend, Paulina Setin. "Like a disaster in a movie."

Concerns about airborne ash after Friday's massive eruption prompted many international airlines to cancel flights to the capital, Jakarta, just days before President Barack Obama's planned trip to Indonesia -- his second stop in a 10-day Asian tour.

All were flying again Monday, and White House officials said Obama was still scheduled to touch down on Tuesday.

Merapi, one of the world's most active volcanoes, has erupted many times in the last century, killing more than 1,400. But Friday was the mountain's deadliest day since 1930, with nearly 100 lives lost.

Islam mandates that the dead be buried quickly, so authorities gave relatives three days to identify their loved ones. To speed up the process, most families chose to have their relatives interred in a mass grave -- a common practice in Indonesia following a disaster.

One by one the bodies -- some too charred to be identified -- were lowered into a massive trench in the shadow of the volcano.

Merapi was still issuing explosive roars Monday as it shot clouds of gas and debris up to 3,000 feet (1 kilometer) in the air as ash and pyroclastic flows poured down its slopes.

"Based on what we're seeing now, it could erupt again any time," said Surono, a state volcanologist.

The National Disaster Management Agency said the overall death toll from the volcano climbed from 138 to 141 on Monday after search and rescue teams found more bodies on the mountain.

The Indonesian government has put Yogyakarta on high alert.

The city's airport was closed yet again on Monday and the ash hung so thickly in the air that breathing became painful and clothes stunk of smoke after any time spent outdoors.

Though there have been no orders to evacuate Yogyakarta, many residents have decided to go on their own. Small hamlets on the edge of the city looked like ghost towns, houses shuttered, some with laundry still hanging outside.

"What choice do we have?" asked Sukirno, 37, as he sped away with his wife and their 8-year-old daughter on a motorbike, saying they would join relatives far away over fears the effect of the ash on their health.

The biggest threat to the city, experts say, is not searing gas clouds, but the Code River, which flows right into the city's heart from the 9,700-foot (3,000-meter) mountain.

It could act as a conduit for deadly volcanic mudflows that form in heavy rains, racing at speeds of up to 60 mph (100 kph) and destroying everything in their path. A thick, black volcanic sludge has already inundated one city neighborhood that starts at the river bank and climbs a hillside.

In Romomangun, the mud burst the banks and poured into buildings.

It has filled a path that runs along the river -- which is usually about three feet (a meter) below a retaining wall but is now even with it. The sludge also rushed into a small, one-room building on the bank that houses a public bathroom. The top of the entry door is now at waist level.

Nearly 280,000 people -- many of whom normally live on the fertile slopes of the volcano -- have jammed into emergency shelters. Many have complained of poor sanitation, saying there were not enough toilets or clean drinking water.

Indonesia, a vast archipelago of 235 million people, is prone to earthquakes and volcanoes because it sits along the Pacific "Ring of Fire," a horseshoe-shaped string of faults that lines the Pacific Ocean.