By Neil Hughes

Published: 01:15 PM EST (10:15 AM PST)

Following the iPad's first full day of sales, Wall Street analyst Gene Munster with Piper Jaffray increased his prediction to between 600,000 and 700,000 sold in the first 24 hours.

Checks with 20 Apple stores found that 19 of them still had iPads in stock at 7:30 p.m. on Saturday. Munster said that's a positive sign, because it means that Apple was able to meet initial demand for the device.

The analyst also noted that there were longer than expected lines at five Apple stores surveyed, including the iconic 5th Avenue store in New York City, where 730 people were in line at 9 a.m. Compare that to just 350 people in line for the iPhone 3GS, and 540 for the iPhone 3G.

"We estimate Apple sold between 600-700k iPads (including online pre-orders which started on March 12th) on the first day (4/3)," Munster wrote. "It took Apple three days to sell a million iPhone 3GS and iPhone 3G's, and 74 days to sell 1m original iPhones. Keep in mind, the majority of sales come on the first day of availability."

Munster had originally predicted that Apple would only be able to produce between 200,000 and 300,000 iPads for the launch weekend. He believed the company would sell through that inventory almost immediately.

Munster's latest numbers fall in line with a report from early March, in which suppliers claimed there were no production issues for the iPad and they would be able to ship between 600,000 and 700,000 at launch. That same report said Apple would be able to ship another million iPads by the end of April.

When Apple began accepting preorders, it limited the number of purchases to two per person, and also turned down volume orders for businesses. These actions fueled speculation of a tight iPad supply for the product's launch.