Building 2 is home to Nomura Securities, among others. According to the Daily News reports the package is thought to contain a grenade.
Update: Though initially worried about what was going on, Nomura employees are apparently “pretty calm right now” and “gathered at a local bar waiting to see what’s next.”
Nomura NY Offices Evacuated Due To Suspicious Package, Traders Say [MarketBeat]
NYPD Investigating Suspicious Package at World Financial Center [Bloomberg]
World Financial Center evacuated after suspicious package found [NYDN]