With many stressed-out travelers still scrambling for train tickets home for Spring Festival, the Ministry of Railways said Wednesday that huge numbers of tickets booked over the phone and not paid for by the deadline are being put back on sale.

An average of 460,000 tickets from all selling systems had been returned to the ticket pool every day during the first three days of the current travel peak, doubling the number of tickets returned during last year's travel rush, the People's Daily reported.

Many travelers who are still hunting for tickets are left wondering why there are so few tickets available one day and then many more are for sale the next. 

The Beijing-based news portal people.com.cn said on Monday the number of tickets available for trains from Nanjing to Wuhan suddenly jumped from several hundred to several thousand on the day of departure.

"It's mainly because the ministry extended the pre-sale period to 20 days, which gives passengers more choices so they are changing their schedules," said Zhao Jian, a professor at the Beijing Jiaotong University, adding that passengers could only book tickets 12 days in advance of departure last year.

Tickets that are not paid for within about 24 hours are put back on sale at 2 pm and at midnight every day, said the ministry. It suggests passengers check the system at these two times for available tickets.

The sudden increase in available tickets, however, has reaped accusations of unfair tickets distribution.

The railway authority in Shanghai said the sudden increase in available tickets can also be caused by a decision to add cars to a train to increase passenger capacity.

Zhao noted that another reason may be the way the railway authority distributes tickets along a train's route. "For example, tickets for a train from Beijing to Chengdu, will also be sold to passengers at stops along the way; but sometimes the railway authority reschedules the station stops and sells all the tickets in one city."

Zhao noted a real-name registration system adopted last year has greatly reduced backdoor ticket selling by railway authorities, adding that more can still be done to make the ticket selling more transparent and fair to the public.

"More ticketing information can be put online, to let the public know in advance about how many seats are available in a train and how many tickets are sold in the city where they live," said Zhao.

Train tickets can be bought through the ministry's online portal, over the phone, at local railway stations and through authorized ticket sellers.