China pressed ahead with military drills near Taiwan and flew drones close to Japan on Friday, escalating tensions in the strait that have threatened to boil over since Taipei welcomed US House Speaker Nancy Pelosi on a historic visit.

Taiwan's defense ministry said Chinese warships and aircraft continued drills in waters around the island, adding that Chinese People's Liberation Army (PLA) forces crossed the median line -- the halfway point between the island and mainland China -- in a move it called a "highly provocative act."

The line has previously been an informal but largely respected border of control between Beijing and Taipei. Taiwan's military responded with radio warnings and put air patrol forces, naval ships and shore-based missile systems on alert, the ministry added.

Two Chinese drones also flew around Okinawa prefecture in Japan on Thursday, prompting the country's Air Self-Defense Force to scramble fighter jets in response, according to a statement from Tokyo's Ministry of Defense on Friday.

In all, 49 planes entered its air defense identification zone (ADIZ), Taiwan's Ministry of National Defense said in a statement. The ministry had previously suggested 68 aircraft flew into the area, but later clarified that 19 operated west of the median line dividing the Taiwan Strait.

The moves comes as China doubles down on rhetoric blaming the US for spiking tensions and forcing it into a response. Beijing announced sanctions against Pelosi and her immediate family and said it would suspend cooperation with Washington on several issues, including fighting climate change, on Friday.