The Centre had earlier ordered deployment of about 10,000 central forces personnel to Kashmir.
Over 280 companies of security forces are in the process of being deployed in the Kashmir valley, official sources said on Thursday.
The security forces, mostly Central Reserve Police Force personnel, are being deployed in vulnerable spots in Srinagar and other parts of the valley, they said.
However, no reason was given for the sudden deployment of over 280 companies (28,000 troops) late in the evening, the sources said.
All major entry and exit points of the city have been taken over by the Central Armed Paramilitary Forces with a token presence of local police, they said.
Officials said that security has been withdrawn from some isolated shrines because of intelligence inputs that foreign terrorists are planning to target police guard there.
Summer vacations have been been preponed at educational institutions and they will be closed for 10 days starting Thursday, they said.
Some langars for the Amarnath Yatra have also been closed, they added.
Local residents have started panic-buying essentials as they are linking the deployment of forces to apprehension of deterioration in the law and order situation.
The Centre had earlier ordered deployment of about 10,000 central forces personnel to Kashmir in order to strengthen counter-insurgency operations and law and order duties.