Vf page and controller

Apex

public class ContactgivenId {
    public List<Account> acct{get; set;}
    public List<Contact> cont{get; set;}
    public String acctid{get; set;}
    public ContactgivenId(){
        acct=new List<Account>();
        cont= new List<Contact>();
        acct=[select id,name from account LIMIT 10];
    }
    public void getContact(){
        cont=[select id, firstname, lastname, phone from contact where account.id= :acctid];
    }
}

VF

<apex:page id="pgId" controller="ContactgivenId">
    <Apex:form >
        <apex:pageBlock >
            <Apex:pageblockSection title="Accounts">
                <apex:pageBlockTable value="{!acct}" var="account">
                    <Apex:column headervalue="Account id">
                        <Apex:outputPanel >
                            <Apex:outputText value="Click" />
                            <apex:actionSupport event="onclick" action="{!getContact}" rerender="contactBlock" >
                                <Apex:param name="accountId" assignTo="{!acctId}" value="{!account.Id}"/>
                            </apex:actionSupport>
                        </apex:outputPanel>
                    </apex:column>
                    <Apex:column headervalue="Account name">
                        <Apex:outputField value="{!account.Name}" />
                    </apex:column>
                </apex:pageBlockTable>
            </Apex:pageblockSection>
        </apex:pageBlock>
        <apex:pageBlock id="contactBlock">
            <Apex:pageblockSection title="Contacts">
                <apex:pageBlockTable value="{!cont}" var="c">
                    <Apex:column headervalue="Contact id">
                        <Apex:outputField value="{!c.Id}"/>
                    </apex:column>
                    <Apex:column headervalue="Contact name">
                        <Apex:outputField value="{!c.firstName}" />
                    </apex:column>
                </apex:pageBlockTable>
            </Apex:pageblockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>