There are now five holes around the city, with fears this will only grow. Residents living close to the craters have been moved away from the danger zone, but the threat remains. Picture: Panoramio

The latest mysterious sinkhole that has appeared in a Urals city has grown in size four-fold in just three months, officials have said.

First spotted on February 17 during routine observations around crater-hit Berezniki, in Perm Krai, it was found to be just five metres in diameter. The fifth hole to have been found in the town in a decade, it was later measured at 7.5metres.

'At the moment the size of the hole is estimated at about 22 metres,' said Andrey Rodionov, head of the department of monitoring and geological exploration for Uralkaliy, the potash fertiliser producer and exporter. 'It has extended due to the sliding of its walls but it is unlikely to have become any deeper, and is still nine metres deep.'

With a population of about 155,000 people, Berezniki is the second largest city in the Perm region and is the location of a number of potassium, magnesium and potash mines.

The latest mysterious sinkhole that has appeared in Berezniki in February 2015. Pictures: Vkurse

The former home of ex-Russian President Boris Yeltsin, it has witnessed a number of accidents, including in the 1980s when water from the Kama River leaked into the mines.

It was after an incident at No1 mine in 2006 that the first of the sinkholes appeared under rail tracks near to Berezniki station. At first management with Uralkaliy tried to fix the problem themselves by building a dam to prevent water from the river reaching the mines.

However, in the end it was decided to flood the No1 mine and abandon it. That did not stop more sinkholes appearing, and another formed at the railway station in 2010.

A year later a large crater formed near to the building belonging to Mine Construction Management. In 2012, during an attempt to fill in the hole, the soil collapsed again and two bulldozers and a truck with a driver fell in, killing the driver.

There are now five holes around the city, with fears this will only grow. Residents living close to the craters have been moved away from the danger zone, but the threat remains.

Sinkholes in Berezniki: 'Grandfather', 'Baby' (formed in 2011) and the sinkhole near Solikamsk formed in 2014. Pictures: Wikipedia, V Solikamske

The original sinkhole, locally called The Grandfather (or also Distant Relative), was initially 80metres long and 40metres wide, but has swelled to a much bigger size.

The building of a school, near to the fifth hole, has been abandoned and the school moved to another location. Officials claim that the hole is not posing any threat but have promised to monitor the situation.

An accident on a mine near Solikamsk city, 30km away from Berezniki, in November is thought to have been responsible for another sinkhole. Fortunately it occurred in the suburbs, in an area not widely populated, and only a few dachas fell into the water.

Last month the Siberian Times also told of the appearance of other holes in the ground in Novokuznetsk, in the Kemerovo, region. The latest measured about 20 metres in diameter, with initial theories suggesting mining subsidence caused the collapse.