A signalling glitch disrupted Blue Line Metro services for nearly an hour during the office rush on Friday morning.

The problem was detected between Dum Dum and Belgachhia stations just before 8.30am, said an official.

A Metro spokesperson attributed the disruption to “urgent unscheduled preventive maintenance work in the auto signalling system”.

Truncated services were operated between Shahid Khudiram (Briji) and Girish Park till the problem was addressed, the carrier said. Trains could not be operated on the section between Dakshineswar and Girish Park.

“Normal services on the entire stretch of Blue Line have resumed,” the carrier said around 9.20am.

The latest disruption in the snag-ridden Blue Line troubled office-goers. A Dum Dum resident takes the Metro to Kalighat, where she works at a private firm.

“I went to Dum Dum and saw that the services were not available. I had to take a suburban train to Ballygunge and then took a bus. The journey took me almost an hour, and it was tedious,” said the passenger. An air-conditioned Metro ride usually takes around 30 minutes to Kalighat.

Ever since commercial operations were suspended at Kavi Subhash (New Garia) station on July 28 following cracks in the platform pillars, the north-south corridor has been under tremendous pressure.

The situation has marginally improved now, but the problem of frequent snags continues to hurt the city’s most popular Metro link.

The ageing infrastructure of the Blue Line, which became operational in the 1980s, is one of the culprits.

The signalling system, the tracks and the tunnels — everything is more than four decades old. As they depreciate, snags will be inevitable, officials said.

The Blue Line needs a complete overhaul, for which the carrier has set the ball rolling. But when it will start has not yet been decided.