Port users have said such navigation restrictions cause congestion in the harbour, resulting in delays in cargo handling and turning around container ships.
The SLPA has tested sonar systems to guard the harbour entrances and had planned to re-open the northern entrance when these systems were fully in place, officials said.
"Once re-opened, the SLPA is aiming to keep the northern entrance open at least during day time," the official said.
The Tiger rebels recently threatened to attack economic targets as security forces closed in on their last remaining strongholds in the island's north-eastern region.
The entrance has been kept closed for years because of the possibility of attack by Tamil Tiger rebels.
It was scheduled to have been re-opened this Thursday but this has been put off after fresh reports of Tamil Tiger threats against the port, officials said.
"Recently, we got information about a possible attack," a senior official said. "If not we had planned to open t