The news adds to concerns over the safety of China's high-speed rail network, which has been dogged by controversy ever since the July 23 collision of two bullet trains killed at least 40 people and left nearly 200 injured.
The Shanghai Railway Station announced that 18 trains running on high-speed rail links - including the new one between Beijing and Shanghai - would be suspended from August 28.
The suspension was due to rescheduling issues, it said in a statement on Sunday, without elaborating. Since the crash, authorities have ordered trains on newly-built fast lines to go slower, impacting the network's timetable.
On Monday, the respected Caixin Century Magazine reported that workers found a 7.1-millimetre-long (0.28-inch-long), 2.4-millimetre-tall crack last month on the axle of a train made by China CNR Corp - a claim the firm promptly denied.
The report comes just 10 days after the state-owned company withdrew 54 trains from the Beijing to Shanghai link, and the magazine speculated that the crack may be the "real reason" behind the recall.
Any axle that has a crack longer than two millimetres must be replaced, according to standards set by the rail ministry. Otherwise, the axle could break and the train may even derail, the report said.
However, Tan Xiaofeng, a spokesman for China CNR Corp, said maintenance workers had just detected a "suspected" crack.
"An expert team from the rail ministry then studied it and concluded it was not a crack," he told AFP, adding none of the trains that was operating on the Beijing-Shanghai fast link had ever had to change axles.
Tan had earlier said the recall of the CRH380BL trains, which led to the cancellation of a quarter of services on the new line, was due to "small but widespread" problems with components including the trains' heat sensors.
The flaws would not compromise safety, but could impact punctuality, he said.
China's high-speed rail network - the world's biggest - is a key political priority but last month's train crash, combined with teething problems on the Beijing-Shanghai link, has been a major embarrassment for the government.