A out-of-control Chinese space station with "highly toxic" chemicals onboard could hit the Earth in 21 days, revised re-entry dates have revealed.

China's first prototype station, Tiangong-1, will come crashing back to the planet -
potentially hitting New Zealand - between March 29 and April 9, experts say, the Daily Mail reported.

The doomed 8.5-tonne craft, which has been hurtling towards Earth since control was lost in 2016, is believed to contain dangerous hydrazine.

While a precise landing location remains unclear, ESA has provided the latitudes between which Tiangong-1 is likely to land. Photo / Supplied
While a precise landing location remains unclear, ESA has provided the latitudes between which Tiangong-1 is likely to land. Photo / Supplied

Agencies around the world who have been monitoring its descent believe it has a higher chance of hitting Europe, the US, Australia and New Zealand.

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They will only know the precise date it will impact and exactly where debris will fall during the finals weeks of its decline.

Experts from the European Space Agency (ESA), based in Paris, are among those tracking Tiangong-1, which means "heavenly palace".

Their Space Debris Office in Darmstadt, Germany, made the prediction earlier this week.

This narrows down from their previous estimate of March 17 to April 21.

In recent days Aerospace, a US research organisation that advises government and private enterprise on space flight, also updated its re-entry window.

It said the space station will enter the Earth's atmosphere on April 3, give or take a week.

Exactly where it will hit is slightly harder to predict, although experts agree it will be somewhere between latitudes of 43° north and 43° south.

The chances of re-entry are slightly higher in northern states in the US, central Italy, northern Spain, northern China, New Zealand, the Middle East and parts of South Africa and southern Africa.

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"Every couple of years something like this happens, but Tiangong-1 is big and dense so we need to keep an eye on it," Jonathan McDowell, an astrophysicist from Harvard University told the Guardian.

While most of it will burn up during re-entry, around 10 to 40 per cent of the satellite is expected to survive as debris, and some parts may contain dangerous hydrazine.

However, due to changing conditions in space, it is not possible to accurately predict where the module will land.

In recent months, the spacecraft has been speeding up and it is now falling by around 6km (3.7 miles) a week. In October it was falling at 1.5km (0.9 miles) a week.

"It is only in the final week or so that we are going to be able to start speaking about it with more confidence," said Dr McDowell.

"I would guess that a few pieces will survive re-entry. But we will only know where they are going to land after after the fact."

Website Satflare, which provides online 3D tracking of more than 15,000 satellites, has calculated what it thinks are the chances of the space station entering the atmosphere during the next three months.

According to its analysis of orbital elements gathered during the last months, the re-enter may occur in March (20 per cent), in April (60 per cent) or in May 2018 (20 per cent).

These predictions may also change as new orbital measurements will be available.

Aerospace Corp has also issued its own forecast over the likelihood of being hit by falling debris.

In a written statement, a company spokesman said: "When considering the worst-case locations, the probability that a specific person will be struck by Tiangong-1 debris is about one million times smaller than the odds of winning the Powerball jackpot.

"In the history of spaceflight, no known person has ever been harmed by reentering space debris.

"Only one person has ever been recorded as being hit by a piece of space debris and, fortunately, she was not injured."

On September 14, 2016, China made an official statement predicting Tiangong-1 would reenter the atmosphere in the latter half of 2017.

Experts from Aerospace's Center for Orbital and Reentry Debris Studies (Cords) have been studying the space station and in November updated their predictions for its uncontrolled re-entry.

The Tiangong-1 spacecraft launched in 2011, with the aim of using the craft to set up a larger space station.

The craft is now at an altitude of less than 300 kilometres (186 miles) in an orbit that is decaying, forcing it to make an uncontrolled re-entry.

Holger Krag, head of ESA's Space Debris Office, said: "Owing to the geometry of the station's orbit, we can already exclude the possibility that any fragments will fall over any spot further north than 43°N or further south than 43°S.

"This means that re-entry may take place over any spot on Earth between these latitudes, which includes several European countries, for example.

"The date, time and geographic footprint of the re-entry can only be predicted with large uncertainties.

"Even shortly before re-entry, only a very large time and geographical window can be estimated."

Much of the spacecraft is expected to burn up in the atmosphere upon re-entry.

But owing to the station's mass and construction materials, there is a possibility that some portions of it will survive and reach the surface.

In the history of spaceflight, no casualties due to falling space debris have ever been confirmed.

WHAT IS THE CHEMICAL ONBOARD CHINA'S SPACE STATION?

A "highly-toxic" corrosive chemical could land on Earth when parts of an out-of-control Chinese space station crash into our planet.

The chemical, called hydrazine, is used in rocket fuel and long-term exposure is believed to cause cancer in humans.

Image shows a 1:1 prototype of the China-made unmanned space module Tiangong-1 in 2010. Photo / Getty Images
Image shows a 1:1 prototype of the China-made unmanned space module Tiangong-1 in 2010. Photo / Getty Images

It is being carried aboard the Tiangong-1 space station which is hurtling towards Earth.

The warning over exposure to the chemical came from Aerospace Corp, a non-profit corporation based in El Segundo, California, which provides technical guidance and advice on all aspects of space missions.

Hydrazine is a colourless, oily liquid or sometimes white crystalline compound with a very highly reactive base.

It has a number of industrial, agricultural and military uses, including in rocket fuel.

Symptoms of short-term exposure to high levels of hydrazine include irritation of the eyes, nose, and throat, dizziness, headache, nausea, pulmonary edema, seizures, and coma, according to the United States Environmental Protection Agency (EPA).

Long-term exposure can also damage the liver, kidneys, and central nervous system in humans.

The liquid is corrosive and may produce dermatitis from skin contact in humans and animals.

Increased incidences of lung, nasal cavity, and liver tumours have been observed in rodents exposed to hydrazine.

The EPA has classified hydrazine as a Group B2, a probable human carcinogen.