The dead included five children. No train passenger of the Ludhiana-Ferozepur Satluj Express suffered any injury in the accident, official sources said.
The ill-fated bus had on board at least 30 passengers, police said. The toll was expected to rise as three of the injured were in a critical condition, they said.
Moga Senior Superintendent of Police L K Yadav said the manned railway crossing was left open by the gatekeeper. "It was gatekeeper's fault as the train was approaching and the bus driver apparently could not see the train due to dense fog", he said.
However, eyewitnesses said the railway crossing at Nu Chur Chak village, where the accident took place, was closed for the passage of 4629 Ludhiana Ferozepur Satluj Express.
"The driver of the bus was apparently in a hurry and got the railway gateman to open the gate," they said. "The bus driver had nearly managed to get past the gate as he had got a part of it already opened. The train arrived just when the gate was being fully opened for the bus to pass through," the eyewitnesses said.
The bus was badly damaged in the accident.
At least 10 injured have been rushed to hospitals at Jagraon and Ludhiana, police said.
Ten bodies, which were taken to Jagraon, were being brought to Moga as the accident site lies in the district. Six other bodies were being brought to the local Civil Hospital where the post-mortem of all bodis would be conducted.
The ill-fated bus was carrying mostly students and teachers, who were on their way to their colleges. Nu Chur Chak village, where the accident took place, lies between Ajitwal and Jagraon.
The Satluj Express had left Ludhiana at around 7.15 am and the accident took place a little after 8.20 am, a railway spokesman said at Ferozepur, the divisional headquarters. Commissioner of Railway Safety will be carrying out an inquiry into the accident, official sources said in Delhi.
Meanwhile, Punjab Chief Minister Parkash Singh Badal announced "adequate compensation" to the families of those killed. An official spokesman quoting the Chief Minister said the state government would bear the cost of the funeral of the accident victims.
The Chief Minister has also announced free medical aid for the injured.