The remaining 30 companies have been withdrawn from other places and rushed to Northeastern states, the officials said.
The troops are from the Central Reserve Police Force (CRPF), the Border Security Force (BSF) and the Sashastra Seema Bal (SSB).
Tens of thousands of protesters against CAB descended on the streets of Assam on Wednesday, clashing with police and plunging the state into chaos of a magnitude unseen since the violent 6-year movement by students that ended with the signing of the Assam accord.
Though no party or student body has called a shutdown, protesters, a majority of them students, fought pitched battles with security forces in the restive state, including in front of the secretariat, the seat of the BJP government.
Police fired tear gas shells and baton-charged protesters, who fought back.
#WATCH Assam: Protests continue against #CitizenshipAmmendmentBill2019, in Guwahati. Police also use tear gas shells to disperse the protesters. pic.twitter.com/5lul19ToTO — ANI (@ANI) December 11, 2019
Assam smouldered with protests rocking several parts of the state on the day the Citizenship (Amendment) Bill is being hotly debated in the Rajya Sabha after its passage by the Lok Sabha.
According to student leaders who went live on national TV, many agitators were injured in police action in front of the secretariat.
All senior civil and police officials were incommunicado but, according to unofficial accounts, hundreds of protesters have been detained in Guwahati and other places like Dibrugarh and Jorhat.
A large number of agitated students blocked the road near the secretariat complex and pulled down the barricade erected on the arterial G S Road, provoking police action.
Police burst teargas shells and baton-charged the protesters, who were seen lobbing back the shells at men in uniform.
They also damaged a stage erected on the road for Prime Minister Narendra Modi's proposed summit meeting with his Japanese counterpart Shinzo Abe on Sunday.
They also pulled down hoardings and banners advertising the government's welfare schemes and made a bonfire of those before the secretariat.
"This is a barbaric government led by Sarbananda Sonowal. We will not succumb to any pressure till the CAB is repealed," a student leader said.
Guwahati: Protest against #CitizenshipAmendmentBill2019 continues in #Assampic.twitter.com/Bmu6LRRKnZ — ANI (@ANI) December 11, 2019
Anti-CAB agitators also clashed with police in Dibrugarh where rubber bullets and tear gas shells were fired to break up protests. A journalist was reported injured in an stone throwing incident in Dibrugarh.
Police chased away agitators who blocked road and rail traffic near Chaulkhowa in Dibrugarh district.
Security personnel also fired rubber bullets and baton-charged the protesters at Moran in Dibrugarh district.
Notwithstanding that no organisation has called any bandh or agitation, spontaneous protests were witnessed in Jorhat, Golaghat, Dibrugarh, Tinsukia, Sivasagar, Bongaigaon, Nagaon, Sonitpur and many other districts since morning.
A motorcycle rally was organised against the Citizenship (Amendment) Bill in Chief Minister Sarbananda Sonowal's hometown Chabua.
Gauhati University, Cotton University and Dibrugarh University postponed examinations scheduled for Wednesday.
Their campuses were deserted with hardly any student around.
The students of Cotton University are continuing their indefinite sit-in since Monday night in the state capital.
Students of Assam Engineering College also came out to protest since Wednesday morning.
Centre starts withdrawing paramilitary forces from J-K, troops moved to Assam Read @ANI Story | https://t.co/7LQnoA7ZMgpic.twitter.com/os46fsjZtS — ANI Digital (@ani_digital) December 11, 2019
Discarded tyres and wooden logs were set on fire as chaos prevailed on highways, disrupting vehicular movement.
In Jorhat and Dibrugarh cities, all shops are closed and vehicles off the roads. People have blocked roads and rail tracks at various places in the two districts.
In Lakwa town of Sivasagar, a huge motorcycle rally was brought out.
Some protesters tried to enter areas where oil wells are located in Lakwa, but their attempts were foiled by police, officials said.
In view of the protests, the Northeast Frontier Railway has cancelled many trains and rescheduled some that originate from the state.
At least 14 trains have either been cancelled, short terminated or diverted anticipating "disruptions in train movement," NF Railway Chief Public Relations Officer Subhanan Chanda said in a statement.