Police said two men on foot set off suicide vests in front of a shopping centre in Burj al-Barajneh, in the southern suburbs of the capital, where the movement is popular.
The Red Cross said 37 people had been killed and 181 wounded in the blasts, which happened around 6:00 pm (1600 GMT), according to witnesses.
An AFP photographer saw extensive damage to buildings around the site of the blast and bodies inside some of the nearby shops.
The blast is the first to target Beirut's southern suburbs since June 2014, when a suicide car bomb killed a security officer who had tried to stop the bomber.
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But prior to that, a string of attacks targeted Hezbollah strongholds throughout the country.
Between July 2013 and February 2014, there were nine attacks on Hezbollah bastions, most claimed by Sunni extremists.
The groups claimed the attacks were in revenge for Hezbollah's decision to send thousands of fighters into neighbouring Syria to support President Bashar al-Assad's forces against a Sunni-dominated uprising.
"I'd just arrived at the shops when the blast went off. I carried four bodies with my own hands, three women and a man, a friend of mine," one man who gave his name as Zein al-Abideen Khaddam told local television.
Another, who did not give his name, described the sound of the two blasts.
"When the second blast went off, I thought the world had ended," he said.