UPDATE 3-Taiwan says U.S. vaccines coming, extends COVID-19 curbs

(Recasts, adds comments from Taiwan president, Chinese government, byline)

By Yimou Lee and Ben Blanchard

TAIPEI, June 7 (Reuters) - The 750,000 COVID-19 vaccine doses the United States has promised Taiwan will be flown in soon, President Tsai Ing-wen said on Monday, as measures to tackle an outbreak that has not yet stabilised on the island were extended.

After months of relative safety, Taiwan has been dealing with a spike in domestic infections and is at its second-highest alert level, with gatherings restricted, entertainment venues shut and students shifted to on-line learning.

Taiwan has been trying to ensure that the millions of vaccines it has on order will arrive sooner, and on Sunday visiting U.S. Senator Tammy Duckworth said the U.S. government would send the island 750,000 doses as part of a broader global donation plan.

"Follow up coordination work for shipping the 750,000 doses of vaccines provided by the United States has already begun, and they will soon be sent to Taiwan by air," Tsai said in a live broadcast from her office, without giving details.

"I promise that the government will do everything in its power to strive for a more stable supply of vaccines," she added.

The brief visit of Duckworth and two other senators angered China, which views Taiwan as its own territory. China's foreign ministry said it had lodged "stern representations" with the United States about the trip.

China has offered Taiwan vaccines, but the government in Taipei has expressed concerns about their safety.

Speaking earlier at his daily news conference, Taiwan Health Minister Chen Shih-chung said the government was still awaiting further details on the U.S. vaccines, but that relevant paperwork should be completed soon.

Around 3% of Taiwan's 23.5 million people have received at least one vaccine shot so far. The government is preparing to ramp up vaccinations, depending on when its orders arrive.

"We didn't buy the vaccines late - we started signing (contracts) from September. The problem at the moment is supplies," Chen said.

The government announced on Monday it would extend its COVID-19 restrictions until June 28 and schools would remain shut until the summer vacation.

"At present the pandemic has not yet stabilised," the Cabinet said.

The extension of the restrictions had been widely expected.

Taiwan will this week start distributing 1.24 million AstraZeneca Plc vaccines donated by Japan on Friday, while the first of 150,000 doses received of the Moderna Inc vaccine will start being given on Wednesday.

Chen announced 211 new infections on Monday, down from 343 the day before. The drop, however, could be due to a lower number of tests at the weekend, he said.

The government has reported 11,491 cases and 286 deaths since the pandemic began. (Editing by Tom Hogue and Jacqueline Wong)