A school bus reportedly full with "screaming kids" has crashed on Queen St in Auckland, causing multiple minor injuries.

A nearby business owner described to the Herald seeing the bus full with screaming children after it smacked into a oncoming car turning right, leaving the bus with a cracked front windshield.

A St Johns Spokeswoman said multiple people were treated for minor injuries and did not require transport to hospital.

Police say it was a minor crash that involved a van and school bus.

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"The road was temporarily closed but has been reopened and we have now left the scene," a police spokeswoman said.

Another crash on Auckland's southbound Southern Motorway near the Papakura off-ramp is causing delays.

NZTA says the left lane was blocked but has now been reopened.

Traffic remains heavy between East Tamaki and Papakura. Drivers are being advised to use an alternative route, or be prepared for a slow trip.

Drivers travelling north on the Northwestern Motorway can also expect delays after a crash blocked the right lane just past the Great North Rd interchange.

NZTA says traffic is heavy between Rosebank Rd through to Lincoln Rd.

Meanwhile, emergency services responded to two serious crashes in Christchurch this afternoon.

One person has been seriously injured after a vehicle collided with a pedestrian at about 2pm in a hotel carpark in Deans Ave.

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In a separate incident, a second person also sustained serious injuries when they smashed into a commercial building on Antigua St at about 2.20pm.

The Serious Crash Unit has been advised of both crashes, and police say they are working to determine the circumstances.