SINGAPORE - Several of Singapore's first China-made MRT trains are being shipped back to their manufacturer for structural defects.

The trains, numbering more than two dozen, are barely five years old.

They were made by China Southern Railway (CSR) Qingdao Sifang Locomotive and Rolling Stock Company, which together with Japan's Kawasaki Heavy Industries, won the first contract here to supply 22 six-car trains for the North-South and East-West lines in 2009 for $368 million.

In response to press queries, SMRT Trains managing director Lee Ling Wee said: "Our engineers discovered that 26 of the 35 trains delivered by the manufacturer had cracks in the structure connecting the car body and the bogie after they were delivered in 2013.

"Since then, we have been working closely with the Land Transport Authority and the manufacturer to rectify the issue.

"The defective trains, which are still under warranty, will be repaired by the manufacturer. All 26 trains will be repaired by 2023."

Mr Lee added that to ensure that the trains are safe for passenger service at all times, "we have been monitoring the defects closely".

"A monthly safety assessment is also conducted by the LTA and manufacturer before the train is put into service," he noted.

The Straits Times understands the episode could derail Singapore's plans to raise its rail service and reliability standards.

According to reports by online news portal FactWire, some of the trains had windows shattering repeatedly, and in 2011, one of the trains' Chinese-made uninterruptible power supply batteries exploded during repair.

While there had been no reported cases of injury, CSR Sifang has reportedly replaced all the batteries with made-in-Germany batteries. These batteries supply power for lights and ventilation during a breakdown.

FactWire said cracks were also found in structural components of trains, including the sub-floor - a compartment under the passenger floor holding the equipment box and electrical wires - and parts connecting the car body to the bogie, the latter having the most serious problems.

Quoting a source from CSR Sifang, FactWire said Kawasaki Heavy Industries was taking over the manufacturing of the flawed aluminium train car body, while the Chinese company will disassemble each recalled train and refit its parts onto the new body.

Kawasaki Heavy Industries (Singapore), which is coordinating the supply of trains from CSR Sifang, was not available for comment.

Meanwhile, Hong Kong's MTR Corp, which has also placed orders with CSR Sifang, told The Straits Times it has not taken delivery of any new trains from the Chinese manufacturer yet.