In a statement to media, the service says strong winds and rain are causing havoc in villages and towns along the southern coast and are expected to continue.
The National Weather Service says Western, Gulf, Central and Milne Bay provinces can expect strong winds and rough seas over the next days.
The landslides and flooding are expected to hit West New Britain province worst.
Airlines, shipping vessels and other travellers in PNG are advised to take precautions over coming days.
In Port Moresby, there was widespread disruption on the roads, power outages and communication breakdowns following widespread storms in and around the National Capital District just days into the new year.
Various reports said the city's drainage system became overloaded by the deluge of water, causing roads to flood and bringing traffic to a standstill.
PNG Power provided continual updates on work it was doing to restore power after the downpours caused blackouts.
PNG Power late last week said that faults had been rectified and supply resumed to Hanuabada, Mobil, POM Tech, Kanudi area, Police Headquarters, Government House and Mining Haus.
Konedobu Feeder three had also been restored enabling power supply to the central business district, Ela Beach, Bampton Street, Davara Motel, Airvos Avenue, Touaguba Hill, Harbour City and Goodman Fielder Flour Mill.
Also late last week, PNG Power was still working on restoring to Korobosea and Murray Barracks, but that was expected to be fixed before the weekend.
Poor weather conditions prevented the swift restoration of power from Waigani Feeder two. PNG Power said a team has started work on it and it was expected to be fixed before the weekend. The feeder covers PNG IPA to Holiday Inn, including North Waigani, Waigani Heights, Ensisi Valley, Savannah Heights and along Waigani Drive to Laguna Hotel, Tokarara, June Valley and Hohola 4.
There is a broken pole at 8 Mile and PNG Power said repairs would take at least two days.
"If you see any fallen power lines or trees on power lines, please report to the Call Centre on 70908000 or 75008000. For more information, contact the National Call Centre on the same numbers," PNG Power said.
Motorist Aaron Chin took a photograph of flooding from his car. "You'd think we are deep in the bush somewhere actually this is in Port Moresby city opposite the Australian High Commission. Government needs to invest in major drainage and sewage upgrades with the population boom. This is just half day heavy rains. Can't just make the outside look pretty," Chin commented.