Shanghai has suspended work on a new metro line on safety concerns, a month after a train collision in the Chinese city injured more than 280 people, state media and the builder said Wednesday.

The move follows complaints to the Shanghai government that workers had skimped on steel reinforcing materials designed to strengthen the underground tunnels for the planned line, the Global Times newspaper said.

The stoppage, though temporary, marks another setback for Shanghai's metro system, still reeling from a crash between two trains which was blamed largely on human error.

The city punished 12 officials over the accident, which happened after a loss of power caused the signalling system to fail and forced drivers to operate trains manually.

A high-speed train crash in the eastern city of Wenzhou, which killed at least 40 people in July, has also heightened fears over the safety of China's rapidly developing transport network.

A spokesman for the builder, Shanghai Tunnel Engineering Co., confirmed the halt in construction on the new line, though he denied media reports that it had been in effect for more than a week.

"The construction site was shut for investigation," he told AFP.

"We are still waiting for a complete investigation report from the government. Only after that can we decide when to resume work."

He declined to comment on the allegations pending the results of the government's probe.

The planned metro line 12 will stretch nearly 40 kilometres (25 miles) between Shanghai's premier Pudong development zone and a western suburb.