Speaking in Taipei, defence ministry spokesperson Sun Li-fang said the scale of the current Chinese naval deployment in an area running from the southern Japanese islands down into the South China Sea was the largest since China held war games around Taiwan ahead of 1996 Taiwanese presidential elections.
China's military has yet to comment and has not confirmed it is carrying out any exercises.
China, which views democratically governed Taiwan as its own territory over the island's rejection, had been expected to launch drills to express its anger at President Lai Ching-te's tour of the Pacific that ended on Friday, which included stopovers in Hawaii and the U.S. territory of Guam.
Taiwan's military raised its alert on Monday after saying China had reserved airspace and deployed naval and coast guard vessels.
"The current scale is the largest compared to the previous four," Sun said. "Regardless of whether they have announced drills, they are posing a great threats to us."
Senior ministry intelligence officer Hsieh Jih-sheng told the same press conference there have so far been no live fire drills in China's seven "reserved" air space zones, two of which are in the Taiwan Strait, but there had been a significant increase in Chinese activity to the north of Taiwan over the last day.
The number of China navy and coast guard ships in the region, which a Taiwan security source told Reuters remained at around 90, was "very alarming", and China was taking aim at other countries in the region and not only Taiwan, he added.
China's deployment in the First Island Chain - which runs from Japan through Taiwan, the Philippines and on to Borneo, enclosing China's coastal seas - is aimed at area denial to prevent foreign forces from interfering, Hsieh said.
INTERNAL SEA
The ministry said China's navy is building two "walls" in the Pacific, one at the eastern end of Taiwan's Air Defence Identification Zone and the other further out in the Pacific.
"They are sending a very simple message with these two walls: trying to make the Taiwan Strait an internal sea" of China, said Hsieh.
Earlier on Tuesday, the defence ministry said it detected 47 military aircraft operating around the island over the past 24 hours, as well as 12 navy vessels and nine "official" ships, which refers to vessels from ostensibly civilian agencies such as the coast guard.
Of the aircraft, 26 flew in an area to the north of Taiwan off the coast of China's Zhejiang province, six in the Taiwan Strait and a further 15 to the island's southwest, according to a map the ministry provided in its daily morning statement on Chinese activities.
A senior Taiwan security source told Reuters that the Chinese aircraft simulated attacks on foreign naval ships and practised driving away military and civilian aircraft as part of a "blockade exercise".
Lai and his government reject Beijing's sovereignty claims, saying only Taiwan's people can decide their future.
China says the Taiwan issue is the "core of its core interests" and a red line the United States should not cross.
China has held two rounds of major war games around Taiwan so far this year.
