Security has been tightened across Tamil Nadu following intelligence inputs that members of the Lashkar-e-Tayiba had infiltrated into the state, police said on Friday.
Coimbatore Police Commissioner Sumit Sharan said the city was under a high alert following information that the terrorists were heading there.
The Indian Air Force station at Sulur on the city outskirts has been brought under tight security cover.
Vehicle screening has been intensified in the vicinity and security checks were conducted at the key facility under the supervision of West Zone IG K Periaiah and District Superintendent of Police Sujit Kumar, police said.
An alert has been sounded in neighbouring Kerala also with police officials mounting an intensified vigil.
Officials in Chennai said security had been beefed up in the state following reports that six members of the terror outfit LeT infiltrated into the state by sea from Sri Lanka and moved to different cities.
Security has been stepped up at many places, including airports, railway stations, bus stands and places of worship across the state.
An alert has been sounded especially in coastal districts to prevent any further possible intrusion, the police said.
Kerala Director General of Police Loknath Behera on Friday directed district police chiefs to keep utmost vigil across the state, an official release said in Thiruvananthapuram.
Chennai Police Commissioner A K Viswanathan said 'storming operations' were underway as part of precautionary steps.
In Coimbatore district, more than 25 check posts have been set up.
Bomb Detection and Disposal Squad was carrying out a thorough check in a leading mall in R S Puram locality in Coimbatore since Friday morning, police said.
Sharan said 10 numbers quick response teams have been put at strategic places just in case to respond if there is any requirement.
"We have put arrangements at all the shopping malls, important temples and all important installations. We have also informed the Army and the Air Force to alert their defences," he told reporters.
The city and its surroundings have come under a tight security cover, with over 2,000 police personnel being deployed, and vehicle check and such checking points enhanced, the police commissioner said. "As of a now, a general red alert is maintained."
Sharan said the police had not released any photographs of any suspects so far as was being telecast in some TV channels, but said searches were on based on information and the description of the suspects.
When pointed out that the developments come close on the heels of the National Investigation Agency action in the city, he said: "There is no need for panic, for worry. What the NIA did was a separate operation (and) this is a separate issue."
The NIA had in June arrested Mohammed Azarudeen, the alleged head of the Islamic State Tamil Nadu module who was a Facebook friend of Zahran Hashim, one of the suicide bombers in the Easter Sunday terror attacks in Sri Lanka in April.
In 1998, Coimbatore was rocked by serial bomb blasts coinciding with the visit of BJP leader L K Advani to the industrial city, leaving 58 people dead and over 200 injured.
Viswanathan told reporters that the police were taking all precautionary measures to avert any untoward incident.
"An alert has been received regarding infiltration of terrorists in Tamil Nadu.... Storming operations are on to ensure no untoward incident happens," the Chennai police chief said.
Police said vehicle audit had been intensified in and around the city.
Though the identity or the nationality of the intruders were yet to be ascertained, sources said one person belonged to Pakistan.
Security has also been beefed up in the temple town of Rameswaram, police said, adding that vital installations and places of worship were being monitored.
The entire coastal stretch in Nagapattinam district has been brought under tight vigil.
The Shrine Basilica at Vailankanni, a famous Christian pilgrim centre, has been provided with additional security cover, the police said.