Property investors in China should hold off on buying and selling homes as the country’s real estate boom hits rockier territory, a top wealth management bank said in a report Tuesday.

High amounts of mortgage debt, overdevelopment and government involvement have put the country, including its top metropolises, in housing bubble territory, according to a report from UBS’s chief investment office. Government intervention in the Chinese economy will likely prevent a rapid price crash, but investors holding real estate there should brace for a prolonged period of cooling.

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Construction and home buying have boomed since 1998, when the government introduced private property ownership.

“Today, both activity and price levels remain at unprecedented heights, despite visible signs of slowing,” according to the report.

Luxury home prices in Guangzhou, Beijing and Shanghai have all slowed their pace of appreciation, according to the most recent Prime Global Cities Index from brokerage Knight Frank.

In Guangzhou, prices grew by an annual rate of more than 35% in the first quarter of 2017, but growth cooled considerably, to around 16%, in the first quarter of 2018.

Residential price growth has also slowed considerably in Shanghai and Beijing, which logged a modest 5% increase in prices between the first quarter of 2017 and the first quarter of 2018, Knight Frank reported.

Still, oversupply is likely to persist, especially considering that the primary buyer population—people ages 25 to 44—is shrinking, according to UBS. There are an estimated 50 ghost cities that exist in China, mainly in the northern parts due to overconstruction.

Two years ago, the Chinese government began introducing cooling measures, including tightened lending rules, but that is unlikely to stem the flood of new product coming online, according to UBS.

Given those conditions, the bank now warns against speculative buying and selling in the Chinese housing market.

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“Capital gains expectations are too high and will ultimately turn negative, at least in real terms,” UBS said in the report.

Rather than attempt to sell units for a profit and risk loss, investors in China should focus on its underdeveloped rental market.

While rental yields remain around 1-2%, they provide real estate opportunity that UBS said “has further to evolve.”