Mount Merapi, Indonesia ? Trains, buses and rented autos were crammed with Indonesians leaving a bustling, ash-choked city of 400,000 at the foot of Mount Merapi, which roared again Monday with explosions of volcanic gas and debris.

Authorities put Yogyakarta on high alert but haven’t ordered evacuations of the university town some 20 miles from the peak. Many residents are leaving on their own, and neighborhoods on the edge of the city looked like ghost towns, houses shuttered, some with laundry still hanging outside.

The city’s airport was closed yet again Monday, adding to the crowds at train and bus stations, and ash hung so thickly in the air that breathing was painful and clothes stunk of smoke after any time outdoors.

“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 Yogyakarta.

After days of failing to get tickets — long lines stretch all the way through the main hall, some people sleeping on their luggage — they decided to rent a minibus with other classmates.

One of the world’s most active volcanoes, Merapi has erupted many times in the last century, killing more than 1,400. It revived two weeks ago and a significant eruption Friday launched hot ash and pyroclastic flows down the mountain slopes that claimed nearly 100 lives, its deadliest blast in 80 years.

Concerns about airborne ash after Friday’s eruption prompted many international airlines to cancel flights to the capital, Jakarta, but all were flying again Monday. White House officials said President Barack Obama still was scheduled to arrive today in Indonesia — his second stop in a 10-day Asian tour.

On Monday, Merapi shot clouds of gas and debris up to 3,000 feet in the air as ash and pyroclastic flows poured down its slopes. Scientists worry the series of eruptions hasn’t eased pressure inside the volcano and instead proves Merapi is unpredictable.