A ball of light followed by a fiery trail of smoke was seen dashing across the night sky in breathtaking videos posted to social media.

Kerrie Fraser and her partner were sitting in their backyard when they noticed the rocket dashing across the sky in Morpeth (Maitland), NSW at 6:45pm on Monday night.

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"I looked up and at first I thought it was a plane going through some clouds but then I thought hang on, there's no clouds," Mrs Fraser told Australian Community Media (ACM).

"Then I saw the triangle shape like mist coming off the back end so it definitely wasn't the plane."

Mrs Fraser said the sighting gave her a "shake up" since she will likely "never see anything like it again in my lifetime".

Mrs Fraser and others across the state pulled out their phones to film the bizarre sighting on Monday night with sightings also in Sydney, Canberra, Silverdale, Forster and Yarrowich.

ANU astrophysicist Dr Brad Tucker said the sighting was likely a Long March 3B rocket launched from China.

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"I didn't see it but I it was visible in Canberra, which is when I got a lot of messages about it," Dr Tucker told ACM.

"As soon as I saw videos I knew it was a rocket plume and so I looked up the rocket launches and sure enough China had launched a Long March 3B shortly before."

China launched a Long March 3B rocket lifted from Xichang Satellite Launch Center at around 6:20pm on Monday before it was seen in NSW and the ACT at around 6:45pm.

Dr Tucker said a number of conditions such as the night sky, weather and temperature made for perfect viewing of the rocket launch.

"Had this been earlier in the day, we wouldn't have seen it," he said.

Dr Tucker explained that the rocket was only seen in NSW and the ACT because of the angle the rocket launched at.

"There's kind of a range where people would see it, so you wouldn't expect people to see if much further north or much further south to see it," he said.

"Sightings have been kind of centred just north of Sydney, around the Sydney area, that means going towards Dubbo, the north coast and then down to Canberra and just south of Canberra but not much further."

China launched two satellite rockets on Monday.

The first was a high-resolution Earth-observation satellite, which was carried by a Kuaizhou-1A solid rocket that launched from the Jiuquan Satellite Launch Center in the Gobi Desert at 5:20pm AEST.

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The second was a classified satellite which was launched Long March 3B - the same rocket that was seen in NSW.

China carried out 39 orbital launches in 2020 - more than any other country including the US, which had 36 orbital launches.

Dr Tucker said he "thinks it's cool that people saw it (the satellite launch) because it's a good chance to highlight a lot of these things are happening".

"Across the earth we're probably seeing one to two rocket launches almost a week now - there's a lot of stuff going up," he said.