The alert was sounded after intelligence inputs that a number HNLC of cadres were trying to sneak into Meghalaya from neighbouring Bangladesh.
"We have received intelligence inputs that a few highly trained cadres of the HNLC are camping in the state that is why we have sounded an alert in all six Khasi Jaintia Hills district," a senior police official said.
Police checkpoints have been set up at strategic location in the city and the affected districts, they said.
Yesterday evening, about 100 posters belonging to the proscribed outfit were seized from a vehicle at Jowai, the headquarters of the West Jaintia Hills district.
Last month armed cadres of the outfit opened fire at a police station in the heart of the city. Two weeks later they opened fire at a police patrol in Jaintia Hills district.
Police have also sought coordinated efforts from the BSF guarding the 443 km international border, parts of which are unfenced, riverine and extremely difficult to man.
The BSF is on 'Ops Alert' from August 6 to 20 in collaboration with their counterparts in Bangladesh to effectively seal the international border.