Warnings are being upgraded, flights cancelled and people told to prepare now for a “complex” severe weather event impacting the NSW coast.

A “bomb cyclone” which has formed off the coast on Tuesday morning could be more severe than initially forecast, experts now say.

The Bureau of Meteorology issued multiple severe weather alerts for gale force winds, flooding rain and damaging surf conditions, as the low-pressure system continues to strengthen and bear down on the coastline.

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Warnings for parts of the state, including Sydney, Newcastle and Wollongong, have been upgraded, with BOM now telling locals to prepare for destructive wind gusts, with possible peak gusts in excess of 125km/h from midday Tuesday, especially for exposed coastal areas between Forster and the Illawarra.

Six-hourly isolated rainfall totals of up to 120mm are also possible, BOM said, with flood watches in place for multiple catchments.

“A rapidly deepening complex low-pressure system is forecast to develop a vigorous coastal low offshore of the Mid-North Coast early this morning,” the warning read.

“(It will then) slowly track southwards and approach the central NSW coast later today before turning and moving offshore into the Tasman Sea on Wednesday.

“Winds are forecast to strengthen along the coastal fringe from this morning, extending to the northern ranges and their eastern lee slopes from Tuesday evening, with a moist southeasterly airstream likely to develop on the southern flank of the system, bringing possible heavy rainfall to the central and southern coastlines.”

The wild weather has disrupted flights in and out of Sydney Airport, with 27 flights cancelled so far.

“With the possibility of severe weather approaching this week, be sure to monitor updates from your airline regarding the status of your flight,” Sydney Airport said.

Virgin Australia said some services on its network have been impacted.

“The safety of our guests and crew is our top priority and our meteorologists continue to closely monitor the weather system,” the airline said.

“We regret the impact of this on guests’ travel plans and are working hard to ensure they reach their destination safely and as soon as possible.

“We encourage guests travelling today and tomorrow to keep an eye on the status of their flight via our website or app.”

Qantas and Jetstar also confirmed disruptions to flights, with both airlines also closely monitoring the weather situation in NSW.

“We’ll communicate directly with passengers if their flight is impacted,” Jetstar said.

What is a ‘bomb cyclone’?

This severe weather event is a rapidly deepening low-pressure system.

When large storms such as this undergo rapid strengthening over 24 hours, they are given the term “bombogenesis” or “explosive cyclogenesis” by meteorologists.

NSW SES crews have warned residents in the path of the strong weather system to “prepare now”.

“Move vehicles under cover or away from trees,” SES said.

“Secure or put away loose items around your house, yard and balcony and keep at least 8m away from fallen power lines or objects that may be energised, such as fences.”

The next warning is due to be issued about 11am on Tuesday.