UPDATE 2-Platinum Underwriters posts Q1 loss

* Platinum Q1 loss $4.20/shr

* Net premiums earned falls 17 pct

* Hanover Insurance Group says weather-related losses to hurt Q1 (Rewrites paragraph 2; adds estimates of quake losses in paragraph 8, details of Hanover Insurance Group's losses in paragraph 11, 12)

April 19 (Reuters) - Reinsurer Platinum Underwriters Holdings Ltd swung to a quarterly loss, hurt by catastrophe losses from earthquakes in Japan and New Zealand, but expects to benefit from better reinsurance rates for the rest of the year.

Reinsurance rates are expected to rise following the major catastrophes in 2011, but the increases are expected to be smaller than the kind after the 2005 storm season, which included Hurricane Katrina.

"The upcoming renewal period will allow us to benefit from a rising rate environment," the property and casualty reinsurer said in a statement.

The Bermuda-based company reported a loss of $157.2 million, or $4.20 a share for the January-March quarter, compared with a net income of $15.4 million, or 34 cents a share, a year earlier.

Excluding certain items, the company reported a net loss of $4.17 per share, while analysts on average were expecting $4.68 a share, according to Thomson Reuters I/B/E/S.

Platinum reported catastrophe losses of $248.1 million for the period, while net premiums earned fell 17 percent to $182.9 million.

Platinum's rivals include Endurance Specialty Holdings Ltd , Everest Re , Axis Capital Holdings Ltd and Allied World Assurance Holdings Ltd .

Risk modeling agency RMS has estimated the total insured loss at between $21 billion and $34 billion, while rivals Eqecat and AIR Worldwide are expecting losses of $12-$25 billion and $20-$30 billion, respectively.

For a factbox on insurance impact of Japan earthquake [ID:nN18236079]

Combined ratio, which is the percentage of premiums an insurer has to pay out in claims and expenses, was 200.4 percent. A combined ratio of over 100 means that the underwriting was unprofitable.

Separately, the Hanover Insurance Group Inc said weather-related losses would hurt its first quarter by 69 to 73 cents per share.

The insurance holding company expects first-quarter segment income in the range of 48 cents to 53 cents per share.

Shares of Platinum Underwriters closed at $37.42 Tuesday on the New York Stock Exchange. Hanover shares closed at $43.60. (Reporting by Tenzin Dekeva in Bangalore; Editing by Gopakumar Warrier)