A view of a gas production plant is reflected in the roof of a car in 't Zand in Groningen February 24, 2015. REUTERS/Michael Kooren

AMSTERDAM (Reuters) - The estimated cost to reinforce more than 150,000 Dutch homes to withstand earthquakes caused by extracting gas in the massive Groningen field was increased to at least 30 billion euros (21 billion pounds), the province said on Monday.

Gas extraction at the field, Europe's largest, which reached more than 50 billion cubic meters last year, is causing increasingly stronger and more frequent earthquakes. The strongest was in 2013 and was 3.6 magnitude.

The report commissioned by the northern Dutch province increased the number of buildings in need of structural improvements to 152,000, up from an estimate of 90,000.

The report published by the Van Rossum research bureau on Monday said the estimated construction cost was 150,000-200,000 euros, more than the value most homes in the region.

A previous report estimated the cost at 6.5 billion euros to reinforce 90,000 buildings.

Production at the Groningen gas field has been increasingly under fire since the Dutch Safety Board censored the government in February for failing to take into account adequately the risk the small earthquakes it causes pose to citizens of Groningen.

Last week, the government said it would immediately implement a court ruling and halt production at Loppersum, part of the Groningen field.

The NAM (Nederlandse Aardolie Maatschappij), a joint venture between Royal Dutch Shell (RDSa.L) and Exxon Mobil (XOM.N) which extracts the gas, has set aside 1.2 billion euros ($1.34 billion) to compensate for damages cause by the tremors.





(Reporting by Anthony Deutsch; Editing by Alison Williams)