Train services in the Sealdah North suburban section will be affected between Friday and Sunday because of the last leg of work to extend five platforms at the station, one of the busiest in India.

Platforms 1 to 5 are being extended so they can accommodate local trains with 12 coaches, instead of nine. Twelve-coach local trains are replacing nine-coach rakes across the country.

The five platforms, which are smaller than the rest of the platforms at the station, are among those that cater to the Sealdah North suburban section, which links Calcutta with North 24-Parganas, Nadia and Murshidabad. Sealdah has 21 platforms in total.

More than 80 trains, most of them in the Sealdah North or Main section (between Sealdah and suburban stations like Naihati, Ranaghat, Hasnabad, Barasat, Bangaon and Krishnagar), will remain cancelled on each of the three days.

Close to 400 trains ply in this section every day, ferrying over 7 lakh passengers, railway officials said.

The trains that run will have a reduced frequency from Friday to Sunday.

On these three days, four pairs of mail/express trains — the Sealdah-Ajmer Superfast Express, Hate Bazare Express, Sealdah-Balurghat Express and Sealdah-Asansol Superfast Express — will originate and terminate at Kolkata (Chitpore) station instead of Sealdah.

The Sealdah-Lalgola Passenger will also originate/terminate at Kolkata station instead of Sealdah.

Around 145 trains will be “short terminated/short originated”, mostly at Dum Dum Junction and Dum Dum Cantonment, said a railway official.

Train services in Sealdah South Section (between Sealdah and Diamond Harbour, Namkhana, Lakshmikantapur, Canning, Budge Budge and Sonarpur) will be unaffected, the official said.

Work on platforms 1 to 5 was long-pending, officials said.

Platforms 6 to 21 are capable of accommodating 12-coach trains. Some were built that way, some had to be renovated. “The work to extend the platforms started in March,” said an official of the Sealdah division.