Three crew members are missing after a well blowout and fire on a platform in China's Bohai Bay this week that has halted operations at China's largest offshore oilfield, where state-controlled giant CNOOC Ltd is partnered by US independent ConocoPhillips.

The blaze hit wellhead platform V on the Penglai 19-3 field on Monday after the blowout in well V29, sources familiar with the incident told Upstream.

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The fire was still raging late on Thursday, the sources said.

The blowout and fire occurred during drilling operations when 102 crew members were on board the platform.

Operator CNOOC Ltd immediately evacuated 99 crew, with three reported missing.

It is not clear if the fire has caused any oil spill.

CNOOC Ltd has not respond to a request for comment from Upstream.

The company has mobilised vessels to extinguish the fire and prevent any potential oil spillage.

The Penglai 19-3 oilfield lies in Bohai Bay Block 11/05 in water depths ranging from 27 to 33 metres. The block also contains the Penglai 19-9 and 25-6 oilfields.

Production at the Penglai 19-3 field started in 2002. CNOOC Ltd holds a 51% operated interest in the fields, with US giant ConocoPhillips holding the remaining 49% equity.

CNOOC Ltd last year produced 165.7 million barrels per day from Bohai Bay.

The company expects to produce a combined 15,681 barrels of oil from Penglai 19-3 and Penglai 19-9 next year.

The field is serviced by the Hai Yang Shi You 117 floating production, storage and offloading vessel.