MILAN, July 11 (Reuters) - Eight of the world"s leading insurance and reinsurance companies on Sunday launched an alliance to help speed up a transition to a net zero emissions economy. The companies, which include Europe"s top three insurers by premiums - Allianz (ALVG.DE), AXA (AXAF.PA) and Generali (GASI.MI) - said the Net-Zero Insurance Alliance (NZIA) would work to shift underwriting portfolios towards net-zero greenhouse gas emissions by 2050. The move comes as insurers come under increasing pressure to spell out how they plan to decarbonise their businesses amid growing calls for them to stop underwriting and investing in fossil fuel projects. read more Each of the companies will individually set intermediate targets every five years and report on progress annually in cooperation with competition authorities, the NZIA members said in a statement. "With this new Net-Zero Insurance Alliance, we are raising our climate ambition further," said Thomas Buberl, Chief Executive of the AXA Group, which chairs the NZIA. NZIA members, which also include Aviva (AV.L), Munich Re (MUVGn.DE), SCOR (SCOR.PA), Swiss Re (SRENH.S) and Zurich Insurance Group (ZURN.S), will set underwriting criteria for the most carbon-intensive activities in their underwriting portfolios and offer solutions for low-emission and zero-emission technologies. They will also include net-zero and decarbonisation risk criteria in their risk management frameworks. "By committing to join the gold standard alliance for net zero, the (NZIA) will ultimately make underwriting contingent on underlying companies having credible net-zero transition strategies," said U.N. climate envoy Mark Carney. The Alliance, first outlined in April, was presented by Generali CEO Philippe Donnet at Sunday"s G20 Climate Summit in Venice. Many of the leading Europe-based insurers have already adopted climate-friendly policies. Last month, Generali pledged to reach carbon neutrality in its direct investment portfolio by 2050. read more