China is quick to criticise nations that show support for the Dalai Lama
China has criticised an invitation from Taiwan to the Dalai Lama, calling him a separatist who wants to sabotage improving cross-strait relations.
Taiwan's president granted opposition requests for Tibet's spiritual leader to comfort victims of Typhoon Morakot.
But a statement from Beijing's Taiwan Affairs Bureau said the Dalai Lama was not a "pure religious figure".
"Under the pretext of religion, he has all along been engaged in separatist activities," the statement said.
"He raises the religious banner and continues to carry out attempting to split the country."
The authorities in Beijing said Taiwan's pro-independence opposition had ulterior motives in asking the more pro-Beijing President Ma Ying-jeou to approve the Dalai Lama's visit.
"Some of the people in the Democratic Progressive Party use the disaster rescue excuse to invite Dalai to Taiwan to sabotage the hard-earned positive situation of cross-straits relations," the statement said.
Under Taiwan's previous pro-independence administration, the Dalai Lama visited the island several times - most recently in 2001.
BBC News, Beijing
It is not a surprise that China has expressed its "resolute opposition" - it objects to most of the Dalai Lama's overseas visits. Beijing believes his aim is to garner support for Tibetan independence.
What is perhaps surprising is that Taiwan's President Ma Ying-jeou has approved the visit. He has worked hard to improve Taiwan's relationship with China since he took office last year. This trip risks undermining those efforts.
But Mr Ma has faced criticism at home recently for what many see as a slow response to the devastation caused by Typhoon Morakot. Many Taiwanese people also say he is just too close to Beijing.
Mr Ma probably gambled that, at this moment, it was better to risk annoying China than his own voters.
But President Ma, who came to power in 2008, is much closer to China than his predecessor Chen Shui-bian.
Last year he refused to grant permission for a visit by the Dalai Lama, saying the timing was not right as his government was working to improve relations with Beijing.
But the typhoon and its aftermath have left Mr Ma in a difficult position.
The Chinese government considers Mr Ma's administration far easier to deal with than the island's previous pro-independence leadership.
However, an estimated 500 people were killed by severe flooding and mudslides caused by the typhoon - the worst Taiwan has suffered for 50 years - and Mr Ma's administration has been criticised for its slow and inefficient response.
His popularity has plunged to a record low of 20% over his handling of the disaster.
According to the BBC's Cindy Sui in Taipei, the president needed to give the green light to the Dalai Lama's visit because he could not afford to hurt his and his party's image any further.
Many relatives of those killed in the south of Taiwan blame the government
So after a five-hour meeting with security officials, he chose to allow the trip.
Correspondents say that harsh Chinese criticism might play into the hands of Taiwan's opposition by reducing Mr Ma's popularity even further.
The Tibetan spiritual leader is due to arrive on 31 August and to stay for four days, with the focus of his trip being entirely to comfort those affected by the typhoon.
The Dalai Lama has long been eager to visit Taiwan, and is looking forward to the trip, his aide told Reuters news agency.
Taiwan is home to a large exiled Tibetan community, and millions of Taiwanese are Buddhists.
A spokesman for Taiwan's Presidential Office insisted "cross-strait relations will not be negatively affected" by the decision.