Shanghai has suspended work on a new metro line due to safety concerns, a month after a train collision in the city injured more than 280 people, state media reported.

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

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

A spokesman for the builder, Shanghai Tunnel Engineering, 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.

“We are still waiting for a complete investigation report from the government,” he told AFP. “Only after that can we decide when to resume work.”

The planned metro line 12 will stretch nearly 40km in a mostly northeast-southwest direction between Jinhai Road in Pudong and Qixin Road in Minhang district.