Libyan forces are patrolling Sirte after seizing control from Islamic State militants.
Forces made up of fighters from Misrata kept advancing this week into the Sirte city centre .
Fighters from the front line in the south of Sirte had looped round to the seafront to capture the port, which lies about 5 km (3 miles) east of the city centre, a military source in Misrata said.
The fighters launched a counter-offensive driving the militant group along the coastal road between the two cities.
The forces are part of the operation supported by the UN backed Unity government which arrived in Tripoli in March and has been working to establish its authority.
The advancement of the brigades has been more swift than expected although hampered by suicide bombers, mines and snipers.
The Unity government has lost about 100 fighters while 500 others have been wounded since the campaign to recapture Sirte began last month.
The Islamic State started advancing into oil rich Libya in 2014 as political turmoil and conflict in the country worsened.