London's FTSE 100 index fell 4.2% to 5,653.2. In Paris the Cac-40 fell 5.5%, and Frankfurt's Dax dropped 5.9%.
Brazil's main index, the Ibovespa, opened 6.0% lower.
Investors have taken little comfort from emergency measures proposed by President George W. Bush on Friday.
Tokyo's Nikkei 225 index slid by 3.9% to its lowest close since October 2005, while India's Sensex shed 7.4%.
"It's another horrible day," said Francis Lun of Fulbright Securities in Hong Kong.
"Today it's because of disappointment that the US stimulus is too little, too late and investors feel it won't help the economy recover."
US markets are closed for Martin Luther King on Monday and will re-open on Tuesday.