"As per the reports, five to six persons were sighted in Pathan suits and appeared to be carrying weapons and backpacks," Naval spokesman Cdr Rahul Sinha said in a statement. Some reports said they were in military uniform.
The alert, which comes four days after the Uri attack which left 18 soldiers dead, has led to elite forces like National Security Guard (NSG), state police's specialised commandos Force One and ATS being roped in for the search and security, highly placed police sources said.
Some children from Uran Education Society's school first spotted the suspects, and their teacher informed the police, the police said, adding none of them have been traced.
The Western Naval Command (WNC) issued a "highest state of alert" along the Mumbai, Navi Mumbai, Thane and Raigad coasts where several sensitive establishments and assets are located.
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Western India's biggest naval base, the Bhabha Atomic Research Centre, fertiliser plants, refineries, power plants and the country's largest container port, JNPT are located in close vicinity of Uran.
The fishing town of Uran is located across the eastern water front of the financial capital. The base located close to the town also houses units of MARCOS, the Navy's elite strike force.
Indian Navy's Chief PRO Capt D K Sharma said the search operation was launched along with Maharashtra police and other agencies.
According to information received by authorities, four school students spotted the men near Uran and Karanja area.
The Maharashtra police has alerted all police stations along the coast, Director General of Police Satish Mathur told PTI here.
Navi Mumbai Commissioner of Police, Hemant Nagarale,
and senior officials rushed to Uran to review the security situation and gathered details from the children, who spotted the men moving suspiciously.
(Reopens BOM17)
Meanwhile, Maharashtra Minister of State for Home (Rural) Deepak Kesarkar said multiple security agencies were involved in extensive combing operations near the naval base in Uran and appealed to people to maintain calm and not believe in rumours.
"We urge people to maintain calm, not to panic or believe in rumours. People should immediately report any suspicious activity in their vicinity to the police," he said.
The minister said the government was quite capable of handling any security situation and deal with forces inimical to the country's interest.
"There is no reason to doubt the information provided by the students. But it needs to be cross-checked. We already have the experience of (tackling) terror attacks in Mumbai," Kesarkar said.
He, however, declined to divulge any further details.
"Some say the suspects were five to six in number, while one student claimed he saw one person. While there were some who claimed the suspects wore 'burqa' (veils), others claimed they were wearing Army fatigues," he said.
According to sources in the Home Department, the NSG, Anti-Terrorism Squad (ATS), Mumbai Crime Branch and Indian Navy are engaged in the combing operations.
Director General of Police Satish Mathur said two students claimed they had spotted suspicious men moving around in Uran.
(Reopens BOM 19)
"Search operation is still on. Navi Mumbai police and coastal police along with the Navy are involved in a search operation which will be carried out throughout night. We have stationed one NSG platoon and 70 commandos of Force One (a state government force) in Navi Mumbai," he said.
The multi-agency and multi-area search operation was triggered by sighing of a few people moving around suspiciously, by a school girl.
"At around 7 AM, a tenth grade girl saw five persons wearing Pathani suits and backpacks which seemed to be having some weapons. She reported this to the school principal," a senior police official told