Hundreds of thousands of New Yorkers applied for Section 8 federal housing vouchers Monday morning, the first time the application process opened after a 15-year hiatus, showing the intense demand for affordable housing in the nation's biggest city.

When New York City opened applications for Section 8 vouchers Monday, the online portal received more than 150,000 applications within its first 12 hours, Bloomberg reported.

The city’s vacancy rate for rental apartments is just 1.4%, the lowest in more than 50 years, according to data released by the city earlier this year. Vacancy rates are even lower for more affordable options.

The window to apply for Section 8 vouchers will remain open for another six days, until 11:59 p.m. on June 9. The New York City Housing Authority is expected to receive more than a million applications before the portal closes, CBS News reported.

Of those applications, NYCHA will add just 200,000 to its Section 8 waitlist, which it aims to finalize by Aug. 1. Around 1,000 households per month will then be chosen to enter into the Section 8 lottery.

The vouchers provide a way for low-income households to pay 30% of a rental's total cost, while the government covers the rest.

The portal to apply for the federal rent subsidy closed in December 2009 after reaching maximum capacity at 128,000 households, The New York Times reported. There are now 3,700 families on the waitlist, according to CBS.

The sprint to apply for vouchers speaks volumes about NYC’s housing and affordability crises, Baaba Halm, vice president for the New York market at Enterprise Community Partners, told Bisnow.

“Based on the numbers alone, the economic hardship and the rent hardship of families in the city is pretty dire,” she said. “It is striking to hear that many applications just today. It's a true reflection of the affordability crisis that so many families need support to pay for their housing costs.”

Part of the reason that it has taken more than a decade to reopen the waitlist is that more households have to rely on Section 8 vouchers for longer, Halm said. While the 421-a extension and new 485-x tax break will go some way to providing new affordable housing supply, she said more help is needed for the most vulnerable New Yorkers.

“You have the affordability crisis, but that is being fed by the stagnation in incomes and economic opportunities,” she said. “We really need more supply, but we also need a way for people to grow their incomes so that they can pay for their housing.”