As thousands protested against the Citizenship Amendment Bill across Assam on Thursday, the Army said it rescued passengers of an express train from a mob trying to set the carriages on fire at Naharkatia railway station in Assam.

An Army spokesperson said the mob had surrounded the Silchar-Dibrugarh Brahmaputra Express at Naharkatia and were in the process of setting it on fire, when security forces intervened.

The railway authorities requested for urgent help to save the passengers, he said.

"Responding immediately, Army and Assam Rifles columns which were on standby rushed to the spot. They immediately took charge of the situation, drove out the mob, managed to rescue the passengers to safety and provided urgent medical attention," he said.

Two people were shot dead in police firing as Assam, the hotbed of anti-CAB protests, plunged into chaos on Thursday with thousands of agitators descending on streets defying curfew, thumbing their nose at Army contingents staging flag marches.

Several towns and cities were placed under indefinite curfew, including Guwahati, the epicentre of protests.