* Gas export halted by crack in pipeline at offshore platform

* Norway export cut to 256 mcm vs planned 300 mcm on Monday

* Outage set to continue on Tuesday

* Timeline for repair still uncertain

* Norway is Europe's biggest supplier of natural gas

OSLO, June 3 (Reuters) - Norway's gas exports to Europe fell sharply on Monday as a shutdown of the offshore Sleipner hub halted operations at the Nyhamna onshore processing plant, pipeline operator Gassco said, lifting European prices to their highest level this year.

The outage was caused by a crack discovered in a two-inch pipeline onboard Norway's offshore Sleipner Riser platform, the company said. It was not yet known how long this will take to repair, but the situation is not considered dangerous, it added.

"This has big consequences from a supply perspective," Alfred Hansen, head of pipeline system operations at Gassco, told Reuters.

The outage at the Equinor-operated Sleipner platform, which began late on Sunday, was set to continue on Tuesday, according to Gassco.

"The field operator will give us a more accurate estimate for how long it could take to repair, and we will then update our forecasts accordingly," Hansen said.

Norway in 2022 overtook Russia as Europe's biggest gas supplier after Moscow's invasion of Ukraine severed decades-long energy ties.

Sleipner Riser is a connection point for the Langeled North and Langeled South pipelines connecting the Nyhamna plant on Norway's west coast with the Easington terminal in northeast England.

Both terminals were shut on Monday, transparency data showed, with Norwegian gas supply nominations falling to 256 million cubic metres (mcm) per day, from 300 mcm/day nominated on Friday, according to Gassco data.

While options exist for bypassing Sleipner, this is time-consuming and not without risk, Hansen said.

Europe's benchmark gas price, the Dutch front-month contract , was up 7.2% at 37.08 euros/MWh by 1322 GMT, easing from an earlier peak of 38.56 euros, its highest level since early December.

Gassco is working with Equinor to resolve the situation, a Gassco spokesperson said separately.

"We are working... with a plan for repairs and with a plan for compensatory measures to deliver the highest possible volume to Europe," the spokesperson said.

While Nyhamna plant operator Shell confirmed the issue was related to Sleipner, an Equinor spokesperson referred any questions on the issue to Gassco.

Nyhamna is able to process up to 79.8 mcm per day, with the current shutdown resulting in a real loss of 56.7 mcm on Monday, according to Hansen. Britain's Easington terminal has a capacity of 72.50 mcm/day. (Reporting by Nora Buli; Editing by Terje Solsvik, Rashmi Aich, Jan Harvey and Susan Fenton)