Traffic congestion faced by Auckland commuters throughout the city's motorway system is starting to increase as breakdowns and crashes force further delays.

Motorists are being warned of traffic on the Northern Motorway heading towards the city due to a crash, clear of lanes, after the Onewa Rd off-ramp.

Meanwhile, a crash is blocking the Greenlane off-ramp on the Southern Motorway heading away from the city centre and delays should be expected back to Newmarket.

Motorists heading southbound are asked to consider using Market Rd or Tecoma St off-ramps as alternative routes, NZ Transport Agency said.

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All other motorways, the Northwestern, Southwestern and Upper Harbour, are free-flowing following a turbulent night of incidents around the city.

Elsewhere, State Highway 29 has been closed for the past three hours following a serious crash in the Lower Kaimai area.

NZTA reports police are hopeful to reopen the road soon, however, it remained closed at 7pm.

Motorists are also advised of the planned closure of SH2 through Karangahake Gorge till approximately 9pm.