Rural fire crews have remained at the scene of a large grass fire in Seddon in Marlborough overnight.

Yesterday the blaze swept across 30 to 40 hectares of grassland north of Seddon at Dashwood Pass, on the eastern side of State Highway 1.

Southern fire communications shift manager Mau Barbara said rural fire crews remained at the scene overnight, with more firefighters due to arrive at the scene this morning.

"They're just dampening down hotspots.

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"With the weather being dry as it is and the wind popping up these hotspots do pop up now and then."

Mr Barbara said fire services would continue to monitor the fire.

At the fire's peak yesterday, a team of around 30 firefighters battled the blaze on the ground, while six helicopters and a fixed-wing aircraft doused the flames from above.

Firefighters managed to contain the perimeter of the fire yesterday afternoon, with ground crews concentrating their efforts on the highest risk point near SH1.

No nearby properties were threatened by the fire, but residents had been warned of the possibility of evacuations if necessary, the fire service said.

The fire also brought several train services on the main trunk line to a halt yesterday.

A KiwiRail spokesman said the Main North Line was cleared last night.

He said one freight service which was also delayed by the closure of the line was cancelled.

Meanwhile most of the 110 passengers on yesterday's Coastal Pacific return passenger trip from Picton, which had been delayed by the fire, were provided with overnight accommodation in Blenheim.

Those passengers needing to make connecting flights yesterday were taken to Christchurch Airport by shuttle, and the remaining passengers would catch a bus to Christchurch this morning, he said.